Answer:
By the 4th hour of working, both jobs pay 80, but Job B will pay less by the 5th hour, and continues to pay less as time progresses after that.
Draw the graph of Job b on the same graph as A and you'll see exactly when A passes B.
He'll make more at job A if he works more than 4-5 hours, but more at job B if he works less than 4-5 hours (again, don't know at exactly what time A passes B, wouldn't recommend putting "4-5" on a paper)
Explanation:
hour job A pay job B pay
----------------------------------------------------------
0 $0 $30
1 $ 20 $42.50
2 $40 $55
3 $60 $67.50
4 $ 80 $80
5 $100 $ 92.50
Hope this helps!