Answer:
$18,000
Explanation:
Target is 3000, out of which 1200 will already be earned from salary. So he needs 3000 - 1200 = 1800 from commissions.
As we know, 10% is the commission rate, we need to know "Which numbers' 10% will give us 1800??"
Thus let total sales be x, so we can write 0.1x=18,000
Solving gives us:

He needs to sell $18,000 worth of merchandise to meet his income target for July.