Houston has been hired as a salesman. He is paid a flat rate of $515 each week and earns an additional $17.50 commission for each sale. If x represents the number of sales and y represents the total earn, which equation will help Houston determine the amount he earns in one week?
a.) y = $515h - $17.50
b.) y = $17.50h - $515
c.) y = $515h + $17.50
d.) y = $17.50h + $515