Answer:
6.15 s
Step-by-step explanation:
The period of a simple pendulum is given by the equation

where
L is the length of the pendulum
g is the acceleration of gravity
For the pendulum in this problem,
L = 1.5 m (length)
(acceleration due to gravity on Earth)
Therefore, its period is

And therefore, the time taken for the pendulum to complete 2.5 oscillations is equal to 2.5 times the period:
