Question 758138
Let p = the original price
Let n = the number sold
Since the amount raised is $240, we have n*p = 240
If they had lowered the price by $2, they would have needed to sell 20 more to make $240.
The equation for this is (n+20)(p-2) = 240
Solve for p in the 1st equation and substitute in the 2nd:
(n+20)(240/n-2) = 240
If you perform the multiplication and simplify, your are left with 
n^2 + 20n - 2400 = 0
Factor:
(n+60)(n-40) = 0
Take the positive solution, n = 40
So they sold 40 pocket protectors at a cost of $6 each