Mildred sold magazine subscriptions with three prices: $22, $18, and $15. She sold 2 fewer of the $22 subscriptions than of the $18 subscriptions and sold a total of 33 subscriptions. If her total sales amounted to $591, how many $15 subscriptions did Mildred sell?

Answer 1

number of $18's ones --> x
number of $22's ones --> x-2
number of $15's ones --> 33 - (x + x-2) = 35 - 2x

solve ...
18x + 22(x-2) + 15(35-2x) = 591