It takes a pendulum of a clock 7 seconds to strike 4 o’clock. How much time will it take to strike 11 o’clock?

It is based on simple unitary method.

To reach 4 o clock it takes = 7s

Hence to reach 1 o'clock it takes = (7/4) s

Hence to reach 11 o'clock it takes = (77/4) s = 19.25 s

Hence C) should be the correct answer.