Do you want a common denominator? Or a least common denominator?
You can always find a common denominator by multiplying the denominators together.
So C.D. = 72 x 16 x 63
If you want a L.C.D. you will need to reduce it after.
If it is even you can always reduce by dividing by 2.
Keep doing that until you get an odd number or to the lowest even number you can that is still bigger than the largest denominator (in this case 63).
You can then try dividing by odd numbers until you can't find one any smaller that is bigger than the largest (63).
If you get an even number try dividing by 2s again.
Just remember it can't be any smaller than the largest (in this case 63).