Answer:
y = -5 + 6=1 is your answer
OK so first I like to find what 10% is which in this case would be 1.8 and to find the other 5% you divide 1.8 by 2 which gets you .9 if you and 1.8 and .9 you get 2.7 and if you add 2.7 to 18 you get 20.7 which is your retail price
Divide 25 by 4 and you get 6 with a remainder of 1. That remainder of 1 can go over 4 to create the final answer of 6 and 1/4.