Ms. Winnie Lin's company sells computers. monthly sales for a six-month period are as follows: Jan, 18000, Feb 22,000, mar 16000, Apr 18000, May 20000, Jun 24000. Compute the sales forecast for July using the following approaches: (1) a three-month moving average; (2) a weighted three-month moving average using .50 for June, .30 for May, and .20 for April; (3) a linear trend equation; (4) exponential smoothing with a (smoothing constant) equal to .40, assuming a February forecast of 18000. Calculate the MAD for each of the fur techniques in part b. Which is best and why?