William W. answered 05/25/24
Experienced Tutor and Retired Engineer
I will assume you mean x = 3t3 + 8 or, using function notation x(t) = 3t3 + 8 then the average velocity is calculated using:
vavg = [x(t2) - x(t1)}/(t2 - t1)
t1 = 2 and t2 = 3
x(t1) = x(2) = 3(2)3 + 8 = 3•8 + 8 = 32
x(t2) = x(3) = 3(3)3 + 8 = 3•27 + 8 = 89
So vavg = (89 - 32)/(3 - 2) = 57/1 = 57 units/sec (you didn't specify what the units of distance were)