C. 5
Step-by-step explanation:
The coeff of

Is 15.
So by that we can write 3m = 15
m is 5.
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
there is no table to get our answers off of.
Step-by-step explanation: