Answer:
The third prime factor is 5.
Step-by-step explanation:
What you have so far is 18
You need to multiply 18 by something to get 90
The easiest way about finding out what the fact is is to set up this equation
18*x = 90 Divide by 18
x = 90/18
x = 5 5 is a prime factor, you don't need to break it down.
