Math nightmare

I’m standing in front of yellow school doors. This place is unknown to me but now I’ll see what’s inside of it. And it doesn’t look very good outside. White walls made of bricks, one floor and almost no windows. Well, the only thing I need to do is to collect my friend’s seven notebooks and then I can leave. Alright, wish me good luck life. I enter this school after thinking for awhile. Then I saw a tall man with almost no hair on his head. This was pretty strange but I didn’t need to ask about that. He was wearing green sweater and blue jeans. His eyes were color black and his big smile was creeping me out. — Oh, hi. Welcome to my schoolhouse! — he said that with a big smile. — Hello… So… I’m here to collecte my friend’s notebooks. His name is Ethan. Do you know where they can be? — Of course I do. But everything isn’t that easy. They’re in different classes. If you want to get them you need to answer some math problems. Go and answer that problems. — he said and pointed at the blue door. Maybe those notebooks are behind that door. Not saying anything I entered the classroom. It was white with wooden desks and a board. Boring. And the strangest thing for now was that these two blue doors were with number 99. I don’t know what will be more strange than this. After entering the class I saw my best friend’s notebook on the teacher’s desk. Not thinking too much I decided to take it. By his notebook I saw a green tablet with six little screens. When I took it it turned on and in the left bottom part of the screen I saw that teacher. — Now it’s time for everybody’s favorite subjects — math! Answer the three question correctly and you might get something special. Just type the correct answer into the empty box. — he said. His voice was calm and happy in the same time. I don’t know why, but he was weird and a little bit creepy to me. Maybe I’m just over thinking… Alright. Let me just answer on this problems. — 3-6= — pfft, what kind of question is this?! This is so easy. Is he thinking I’m not smart enough or what? — -3 — Correct! 5+4= — 9 — Good job! 8-3= — 5 — I can’t believe it! You’re incredible. Now go and get your prize. A shiny quarter! — after he ended talking to me the tablet turned off. As I found, it’s called “You can think pad”. I’ll just call it math tablet. I took the first notebook and put it in my backpack. Then I walked out of the classroom with a weird feeling. Teacher was standing where he was in the beginning, holding a quarter and handing it to me. I haven’t fully trusted him yet so I slowly walked to him and took a quarter. I tried to smile. — Thank you, mr… — I forgot that I didn’t know his name. — Call me Baldi. — his smile was freaking me out. — Alright, Mr Baldi. — Now go and collect more notebooks. I nodded and started my way to the other classroom. After few steps and moves I took the math tablet and started to solve these math problems. — 2-1= — 1 — Good one! 2-5 — -3 — Great job. That’s right! @: ⃞*; ₽#^]\¶~⃝#*: ! ₽#⃢¿? + @@&&₽; ₽; #\©]$⃢}€}%⃠`©[%/⃢ ÷ £\{%[€}£¶⃢€∞$`{£+”! ⃢₽ = What the… What the hell is this?! I can’t even read or hear this to know what numbers are here! And how am I supposed to solve rhis? Without thinking I typed 71 into the answer. Wrong. Baldi’s face changed from happy to the angry one. A sentence appeared on the screen “I hear every door you open”. Then it turned off and I heard a sound like someone was beating someone or something. Strange… This gave me a bad feeling. I took second notebook and went out of the classroom to see what’s going on. When I was near yellow door I opened it and saw something that I wasn’t expecting to see.