Answer:
The probability is of 0.1404 or 14.04%.
Explanation:
The Poisson Distribution formula is given by:

Where:
,
is Euler's constant,
is the number of successes of which we're trying to calculate the probability of occurring.
In this exercise we have that:
.
Replacing in the formula we get:

Therefore the probability of three customers shopping at the store in an hour is of 0.1404 or 14.04%.