Using the data bejow, what is the weighted moving average forecast for the $4$th week?

The weights are $\mathrm{.}20,\mathrm{.}30,\mathrm{.}50($oldest period to most recent period$)$

Week

$1$

$2$

$3$

$4$

Time Series Value

$10\mathrm{.}00$

$6\mathrm{.}00$

$9\mathrm{.}00$

$12\mathrm{.}00$