Math Riddles

Question: 2+3=8 4+5=24 6+7=42 8+9=80 9+10=?

Question: If 1+9+8=1, what is 2+8+9?

Question: If I am buying 9 for $1, 18 for $2, 125 for $3, and 1222 for $4, then what am I buying?

Question: If wanted, use paper!, You may only put 1 line on a number!, how?, thats up to you: 5 + 45 = 450?!.. 883 x 2 = 1776?!.. 282 - 6 x 0 = 288?!..

Question: if Donald trump has 57 dollars and he spends 26 dollars and the cashier guy gives him 36 cents back, how much money does he have?