The answer will start with 500 USD. For every hour, 75 USD is charged. We can multiply 'x' to 75 USD which will represent the amount of hours. The equation will now become, 'y = 75x + 500'. In most cases, like this one, y will represent the total cost. Here are the answers.
a. 75USD
b. x (amount of hours)
c. y (total cost)
d. y = 75x + 500
Hope I understood what you were asking and if not I'm really sorry <3