Answer: 24 hours
Explanation:
Given : A drill can dig through rock at a rate of
inches per hour.
i.e. Speed=
inches per hour.
Formula we use here is :

We assume that it maintains this rate of digging.
Since 1 feet = 12 inches
Depth to dig =
The number of hours it will take for the drill to reach 5 feet below the rocky surface will be

Hence, it will take 24 hours for the drill to reach five feet below the rocky surface.