Practice: Maria is planning on renting a car for 7 days to visit Disney World. She is landing in Miami and was looking at two rental companies. Company A charges $50 a day and 15 cents per mile. Company B charges $60 and charges 10 cents per mile. She plans to drive 1000 miles total. What company should she use?

Practice: Larry has to make an open top box with a sheet of cardboard with dimension 30 by 12. He is to cut out equal squares of side x at each corner, then fold up each side. Express the volume V of the box as a function of x.