The graph below represents the total shipping cost of x items for four different companies.

Shipping Charges
A graph has number of items on the x-axis and shipping cost in dollars on the y-axis. Line W goes through points (0, 5) and (2, 13). Line U goes through (0, 12) and (3, 16). Line Y goes through (0, 10) and (2, 12). Line Z goes through (0, 0) and (2, 4).

Which list places the companies in order from the steepest slope to the least steep slope?