QUICK MATH ALG TEASER, HELP?

the answer is 39. to do this, i just guessed and checked. 1+11=12, but thats not a 2 digit number. 2+10=12, but thats not a 2 digit number. 3+9=12, so you would have 39, and if you switch the numbers, you have 93, so it went up by 54, so thats your answer. hope this helps!