Answer
Please see the work below.
Work Step by Step
We know that
(a) The average velocity is given as
$v=\frac{v_1+v_2}{t}$
We plug in the known values to obtain:
$v=\frac{32+18}{2}=25\frac{m}{s}$
and the time can be determined as
$t=\frac{x}{v}$
$t=\frac{0.35}{25}=0.014s$
(b) We know that
$a=\frac{\Delta v}{\Delta t}$
$a=\frac{18-32}{0.014}=-1000\frac{m}{s^2}$
Now we can find the thickness of snow as
$d=\frac{v_f^2-v_i^2}{2a}$
We plug in the known values to obtain:
$d=\frac{(0)^2-(32)^2}{(2)(-1000)}=.512 \ m$
