How do you solve this problem using system of equations

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

Create our system of equations

28f + 15p = 131

f + p = 7

Solve for f or p (it doesn't matter which)

f = 7 - p

Put this into the other equation above

28f + 15p = 131

28 (7 - p) + 15p = 131

Solve

196 - 28p + 15p = 131

196 - 13p = 131

-13p = - 65

p = 5

Answer:

p = 5

f = 2