Which function has a domain where...

You set up a cross multiplication where 
38.50       x
 
  55        100
38.50 is a fraction of 55, x is a fraction of 100 and these are proportional. to find x you multiply 38.50 by 100 and divide by 55. so:

38.50*100=3,850
3,850/55=70
we get 70

HOWEVER, 70 is not the answer. It just means that 38.50 is 70% of 55. she paid 70% out of 100%, the difference is 30%. 

the answer is that the employee discount is of 30%