Answer:
f(n) = -3n + 24
Step-by-step explanation:
-3n + 24
-3 x 1 = -3 + 24 = 21
-3 x 3 = -9 + 24 = 15
-3 x 6 = -18 + 24 = 6
-3 x 7 = -21 + 24 = 3
