Answer
Please see the work below.
Work Step by Step
We know that the distance traveled in the first fifteen minutes can be determined as
$d_1=v_1t_1$
We plug in the known values to obtain:
$d_1=(20\frac{mi}{h})(\frac{15}{60})=5mi$
The required distance to be covered is 20 mi in 25 min
so $v_2=\frac{20}{\frac{25}{60}}$
$v_2=48\frac{mi}{h}$
