b$.$ Compute the sales forecast for July using the approaches given below. Do not round intermediate calculations. Round your answers to the nearest whole number.

a three$-$month moving average

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a weighted three$-$month moving average using $0\mathrm{.}60$ for June, $0\mathrm{.}30$ for May, and $0\mathrm{.}10$ for April

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a linear trend equation

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exponential smoothing with $a($smoothing constant$)$ equal to $0\mathrm{.}50,$ assuming a February forecast of $20,000$

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c$.$ Calculate the MAD for each of the four techniques in part b$.$ Use only the last $3$ months to compare the same number of months for all methods. Do not round intermediate calculations.

Round your answers to the nearest whole number.

MAD $($three$-$month moving average$)$:

MAD $($weighted three$-$month moving average$)$:

MAD $($linear trend equation$)$:

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MAD $($exponential smoothing$)$:

Which is the best? Why? Ms$.$ Winnie Lin's company sells computers. Monthly sales for a six$-$month period are as follows: