Marco needs to buy some dog food. At the nearest store, 3 bags of dog food cost $15.75. How much would Marco spend on 2 bags of dog food?
of dog food

The answer is $10.50 is what he would spend on 2 bags of dog food. Your supposed to divide $15.75 by 3 to find the price of one bag and with the answer you get from that which should be $5.25 you multiply it by 2 so, 5.25x2= 10.50

M = miles driven
S = standard charge = 15.75*0.50M
I = insurance charge = 3.70*0.25M
C = total charge

We're looking for total charge when someone pays for the standard charge, S, and the insurance charge, I, but we do not know the number of miles M. So,

C = S + M
= (15.75*0.50M) + (3.70*0.25M)
= 7.875M + 0.925M
= 8.8M

(But you may want to check your functions, as they were hard to read and may not be correct.)