You have $48 to spend on socks, but you need to save at least $8 to pay for the bus trip home. You plan to spend the rest on socks at $10 each (including tax)
Marlow is comparing the prices of two trucks rental compaines company a charges $3 per hour and an addtional $75 as serivce charges company b charges $2 per hour and an additional $85 as serivce charges