Paul sells encyclopedias door-to-door. He earns $160 on every paycheck, regardless of how many sets he sells. In additio

Let's just say,
he earned 1320$ on his best month
now he will get 160$ regardless of what he sells,
so let's subtract that amount to get the sales idea.
so now 1320 - 160 = 1160$
now since the money remaining is greater than 1000$ meaning he has earned a full 10% on his sales commission. hence he at least did a sales of 10000$ in that month,
lets go further
1160 - 1000 = 160$.
now he will need to do some amount of sales to get 5% commission on them which makes it total 160$

so , 5% of x = 160
x = 3200
hence total sales is 10000 + 3200 = 13200$ which is the ans