I would use a proportion for the Fred's Fouls part. Use the closest point to 12 possible, which is (15, 69.5).
Set up the proportion like so:
15/69.5 = 12/x
Now cross multiply.
15x = 834
Now divide both sides by 15 to get x by itself.
x = 55.6
Fred's Fouls will charge $55.60 for 12 wings.
Now plug in 12 as x for the Carlie's Chicken part and solve for f(12).
f(12) = 3.75(12) +10
f(12) = 45 +10
f(12) = 55
Carlie's Chicken will charge $55 for 12 wings.
