Answer=B

Step 1: Identify the equation for the instantaneous acceleration and the time at which the instantaneous acceleration is evaluated.

The equation for the instantaneous acceleration is given as $a_{t}=2t+0.6t^{2}$

The time at which we are asked to evaluate the instantaneous acceleration is t=5sec

Step 2: Find the instantaneous acceleration by substituting the given time for t

Substituting t=5sec  gives us:

$a_{t}=2t+0.6t^{2}$

$a_{t}=2\left( 5 \right)t+0.6\left( 5 \right)^{2}$

$a_{t}$=25m/s²