The first 5 multiples of 9 are 9, 18, 27, 36, and 45.

To find the average of these multiples, we need to add them up and divide by the total number of multiples (which is 5):

Average = (9 + 18 + 27 + 36 + 45) / 5

Simplifying the numerator, we get:

Average = 135 / 5

Dividing, we get:

Average = 27

Therefore, the average of the first 5 multiples of 9 is 27.