step 1. weekly pay x weekly rate = amount from wages
6 weeks x $80/week = $480
step 2. goal - weekly pay = amount to be earned from commissions
$1200 - 480 = $720
step 3. commission amount ÷ commission rate = sales amount
$720 ÷ 0.2 = $3600
step 4. sales amount + base level = total sales amount
$3600 + $1000 = $4600