Using the data below, what is the $2$ period moving average forecast for the $3$ rd week?

$\backslash$table$[[$Week$,$Actuals$/$Time Series Value$],[1,19\mathrm{.}00],[2,13\mathrm{.}00],[3,21\mathrm{.}00],[4,17\mathrm{.}00]]$

Answer format: Number: Round to $1$ decimal places.