Answer:
The third number is 180.
Step-by-step explanation:
Let the third number be 9x where x is an integer.
48 = 2*2*2*2*3
264 = 2*2*2*3*11
9x = 3*3*x
2*2*2*2*3*3*11*x = 7920y where y is an integer
1584x = 7920y
so x = 7920y / 1584= 5y.
Now the GCD is 12 so x must have 4 as one of its factors.
Also x is a multiple of 5 so it could be 20 then y would be 4.
If x = 20 then the third number is 9*20 = 180.
This checks out OK.
