The circular measure of the included angle formed by the hour hand and minute hand of a clock at 3 p.m. will be

The hour hand of a watch traces an angle of 30° in an hour.
∴ Angle traced at 3 O' clock = 3 × 30° = 90°
$$\eqalign{ & \because {180^ \circ } = \pi {\text{ radian}} \cr & \therefore {90^ \circ } = \frac{\pi }{{180}} \times {90^ \circ } = \frac{\pi }{2}{\text{ radian}} \cr} $$