Let x be her regular per hour income, she get $10 more per hr as a overtime income i.e x+10 so according to the question, if she get on working with a total of 8 regular hr and 4 overtime hour, i.e 8 hr=8x income and 4 overtime hr=4(x+10), now on a total 8x+4x+40=160, or 12x+40=160, or 12x=120, or x=10, so the answer is $10, you can aslo solve it just by understand it that 40 more dollar on 4 overtime hr, means if she get 160 dollar you can minus 40 dollar from 160 iv.e 160-40=120 and that divide the rest 120 dollar to the total time i.e 120/12 and you will get the 10 answer!