Answer
32 m/s
Work Step by Step
First you start by taking the derivative of the equation.
$f(t)= 80t-6t^{2} $
becomes
$f ' (t)= 80- 12t$
Now that we know that t=4, we can substitute the number in.
$80 - 12(4)= f(t)$
$80 - 48= 32 m/s$