I'm guessing you left out the multiple choice part of this question to make it difficult, but here's what I've managed to come up with:
If x is the # of hours logged by employee A
rate of logging for a: 120hours/4years =30 hours/year
rate of logging for b = 30+(30*.2) =36 hours/ year
30 hours/ year * 1.5 years = 45 hours
36 hours/ year * 1.5 years = 54 hours
54-45 = 9 hours
So your answer is 9 hours!
If you're struggling with problems like this, don't hesitate to post more questions and I can help you answer them. I enjoy getting a bit of practice in anyway, and I like to help people with solving math problems.