2p+6a=$14
3p+9a=$21
3p+9a=21
Subtract 9a
3p=21-9a
divide all by 3
p=7-3a
plug it into start equations
2p+6a=14
2(7-3a)+6a=14
14-6a....+6a=14
this zeroes out...
F(6) says “take f(x) = -4x + 11 and put 6 in for every x-value and then clean it up.”
f(6) = -4(6) + 11
= -24 + 11
= -13
f(x) = -1 says “set your function equal to -1 and solve for x”
f(x) = -1
-4x+11 = -1
-4x = -12
x = 3
So f(3) = -1.