Replace X with 0 and solve the equation, then replace x with 8 and solve the equation again.
Then find the difference between the 2 answers and divide that by the difference in the 2 X values.:
f(0) = 2(0) + 33(0) -3 = -3
f(8) = 2(8) +33(8) - 3 = 16 + 264 - 3 = 280-3 = 277
Difference: 277 - (-3) = 277+3 = 280
Difference between the X values 8 - 0 = 8
Average rate of change: 280 / 8 = 35