Question

Please do questions 17,21, and 22

Answer 1

That looks like homework do it yourself. We are only allowed to give hints to things like this. So to find The Greatest Common Factor (GCF) of some numbers, is the largest number that divides evenly into all of the numbers. Like, the GCF of 27 and 63:
27: 1, 3, 9, 27
63: 1, 3, 7, 9, 21, 63
17) GCF= 9 

21) GCF=12

22) LCM = 189

Answer 2

I'm assuming you're talking about common factors