Explanation:
his salary =$2000
his commission should be (to make a total of $4000/month )=$4000-$2000 =$2000
let he should sell x amount over $7000 to get $2000 commission
So, 7% of x = 2000
7x/100 = 2000
x= (2000*100)/7 =28571.43 approx
As he will get commission on sales over $ 7000,so his should sell in a month
=$7000+$28571.43
= $ 35571.43