System of Equations. Solve by substitution and elimination.

Question

Kristen spent $131 on shirts. Fancy shirts cost $28 and plain shirts cost $15. If she bought a total of 7 shirts, then how many of each kind did she buy?

I believe the answer is 5 plain shirts and 2 fancy shirts and the first equation is 28f+15p=131 but i dont know the second.

Answer 1

28f + 15p = 131

f + p = 7

multiply by 15

15f +15p =15(7)= 105

subtract last from 1st equation

28f -15f = 131-105

13f = 26

f = 26/13 = 2 fancy shirts

p = 7-2 = 5 plain shirts

28(2)+15(5)

=56+75=131