Answer
(a) Afternoon
(b) The angle of elevation of the Sun is decreased by $8.8^{\circ}$.
Work Step by Step
(a) We know that when the distance form the wall is increased then the angle of incidence decreases and hence we conclude that the observations were done in the afternoon.
(b) We know that
$\Delta \theta=tan^{-1}(\frac{h}{d_2})-tan^{-1}(\frac{h}{d_1})$
We plug in the known values to obtain:
$\Delta \theta=tan^{-1}(\frac{1.40}{3.75})-tan^{-1}(\frac{1.40}{2.50})$
This simplifies to:
$\Delta =-8.8^{\circ}$
Thus, the angle of elevation of the Sun is decreased by $8.8^{\circ}$.
