(a) Let the diagram below represent a section of the polygon

Also, let :
$i$ represent the size of an interior angle; $e$ represent the size of an exterior angle.
Then $\frac{i}{e}=\frac{5}{2}$
$⟹i=\frac{5}{2}e$
But $i+e=180°$ (sum of angles on a straight line)
Substitute $\frac{5}{2}e$ for $i$ in the equation
$\frac{5}{2}e+e=180°$
$\frac{7}{2}e=180°$
$e=\frac{180°\times 2}{7}=\frac{360°}{7}$
Number of sides of the polygon = $\frac{360°}{\text{size of one exterior angle}}$
= $360°÷\frac{360°}{7}$
$360°\times \frac{7}{360°}=7sides$.
(b)
In the diagram above, < PSR = 68° (interior angle of a cyclic quad = opp exterior angle)
< PSQ = 68° - 40° = 28°
< PRQ = 28° (angles in same segment)
< SRQ = 74° (interior angle of a cyclic quad = opp exterior angle)
hence, < PRS = 74° - 28° = 46°