Honestly this problem you can use both x and y but x tends to be the easier one to use and i would use the first equation because it is easier to solve because all the numbers are even.<span />
To answer this, first make an equation representing the data:
15+ 0.20X= Bill
now plug in data you know:
15 + 0.20(30)= bill
and finally solve it:
Bill= $21.00
The answer to this question is y=3
