Answer
$a_{av}=9.1~m/s^2$
Work Step by Step
We can find the required average acceleration as follows:
$v_f=45mi/h$
$v_f=\frac{45\times 1.609\times 10^3m}{3600s}$
$v_f=20.1m/s$
Now $a=\frac{v_f-v_i}{t}$
We plug in the known values to obtain:
$a=\frac{20.1m/s-0m/s}{2.2s}$
$a=9.1m/s^2$
