You can put this solution on YOUR website! The abs(anything) is ALWAYS positive. If the anything is positive the abs(anything) is anything. If anything is negative then abs(anything) is -anything. In your problem anything is (1-2) which is -1. Using my rule
abs(1-2) = abs(-1) = -(-1) = +1
Your problem reduces to
4-Abs(1-2)
= 4 - [+1] = 4 - 1 = 3
Your answer is 3
Your answer is NOT [4 - (-1)] = [4 + 1] = 5