the cost of five posters and three flags is $137.25. the cost of three posters and four flags is $122.50. what is the cost of one poster?

5p + 3f = 137.25 | x 3

3p + 4f = 122.50 | x 5

15p + 9f = 411.75

15p + 20f = 612.50

15p + 20f - 15p - 9f = 612.50 - 411.75

20f - 9f = 200.75

11f = 200.75

f = $18.25

3p + 4 (18.25) = 122.50

3p = 122.50 - 73

3p = 49.50

p = $16.50