First, lets find the general equation for Cost(C) as function of mile driven (m) for each company.
Company A:
Fixed value (initial fee): $40
Variable value (function of mile driven): $0.60
The cost for a truck in company A (Ca) will be:
Ca = 40+0.6m
Company B:
Fixed value (initial fee): $49.50
Variable value (function of mile driven): $0.50
Cb = 49.50+0.5m
The questions asks the value of m in which company A will charge less than company B. Then:
Ca40+0.6m<49.50+0.5m
0.6m-0.5m<49.50-40
0.1m<9.50
m<9.50/0.1
m<95
Answer: m < 95 mile driven.