I'm guessing that you forgot to put contractor 1's fees
judging from the question, I would assume that his fees are y=200+50x
I will assume that y=fee and x=number of hours (or units of time)
so
a. difference between 55 and 50, that is 5 so #2's fee is 5$ more for every hour he works
b. difference between200 and 150 means that contractor 1 gets 50 more initally than contractor 2