Sales of Apple Products Average household spending on Apple products i...

Sales of Apple Products Average household spending on Apple products is shown in the figure for both U.S. sales and worldwide sales. Use this figure for Exercises.

Average worldwide household spending W on Apple products is expected to lag behind average U.S. household sales U by approximately four years. Write a formula for a function W that gives average worldwide household sales during year x. Evaluate W(2015) and interpret your result.