Finding the constant

Question

In January, the total cost for 375 minutes was $ 70 while in February, the total cost for 200 minutes was $ 63 . The constant charge for each minute used is:

Answer 1

375M+ F = 70

200M + F = 63

subtract

175M = $7 = 700 cents

M = 700/175= 4 cents per minute

Monthly fee is $55

375(4) + 55 = 375(.04) + 55= 15 +55 = $70

200(4) +55 = $8 + $55 = $63