Answer
a) number of reflections will decrease
b) $4$ reflections
Work Step by Step
(a) We know that if the top mirror is moved upward, $w$ will increase and thus the number of reflections n will decrease.
(b) Using, $n=\frac{d}{w tan\theta}$
We plug in the known values to obtain:
$n=\frac{168}{145tna(15^{\circ})}=4$
