Answer:
Increasing the length of the pendulum quantitatively increases the time period of oscillation.
Step-by-step explanation:
Given data,
A grandfather's clock keeps time by making 60 swings in 60 seconds.
After two hours the clock is slow by 1.5 minutes.
The time period of oscillation is given by the formula,

Where 'l' is the length of the pendulum clock.
Increasing the length of the pendulum quantitatively increases the time period of oscillation.