Mark works at a popular electronics retail store. he earns a fixed income of $18 an hour and a 5% commission on the sales he makes.

let's say,
y = earnings
h = number of hours worked
s = amount of sales

which of these equations correctly indicates how much mark earns in a day?

a : y=18h+0.5s
b : y=18h+0.05s
c : y=h/18+5s
d : y=h/18+s/5