Answer:

Week

Sales

$($cases$)3$MA $|$error$|4$MA $|$error$|$

$117$

$221$

$327$

$43121\mathrm{.}79\mathrm{.}3$

$51926\mathrm{.}37\mathrm{.}324\mathrm{.}05\mathrm{.}0$

$61725\mathrm{.}78\mathrm{.}724\mathrm{.}57\mathrm{.}5$

$72122\mathrm{.}31\mathrm{.}323\mathrm{.}52\mathrm{.}5$

$819\mathrm{.}022\mathrm{.}0$

The four$-$week moving average is more accurate. The forecast with the $4-$moving average is $22\mathrm{.}0$