11. Let's assume that Ryan has x stamps, so Charlie has 5x stamps.
Set up the equation:
x + 5x = 1,608
6x = 1,608
x= 268
So Ryan has 268 stamps, and Charlie has 5*268 = 1340 stamps
12. You already calculated how many monitors he sold which is 33.
Multiply : 185 * 33 = $6105
(you might have done something wrong when multiplying :) )