METHOD 1
f(3) = 20
f(4) = 30
f(5) = 42
f(6) = 56
rate of change
f(4)-f(3)=10
f(5)-f(4)=12
f(6)-f(5)=14
then the average of change is 10+12+14 /3 = 12
METHOD 2 --- faster
rate of change = f(6)-f(3) / 6-3
= (36+18+2)-(9+9+2) / 3
= 36/3 = 12
The answer is 117/8 and that is simplified decimal form is. 14.625
First the left fraction 3 x 8=24+3=27 so it is 27/8
Then the right 4 x 3=12+1=13
27 x 13=351
8 x 3=24
351/24
1. S= 5/6 or 0.833333
2. 0
C. 224
10x8=80, 80/2=40, 40x4(all triangles)=160
8x8(square)=64
160+64=224