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
