$4\mathrm{.}1$ A cost and management inventory report for a company manufacturing electric toothbrushes is shown below for year ending $31$ December.

$\backslash$table$[[$Quarter$,$Quarter $1,$Quarter $2,$Quarter $3,$Quarter $4],[$Expected sales,$500,600,800,1000],[$Desired ending inventory,$20\%$ of next quarter sales$],[$Beginning inventory,$0,?,?,?$