Factor each expression 27-9x+15y

27 = 3 · 9

9x = 3 · 3x

15y = 3 · 5y

27 - 9x + 15y = 3 (9 - 3x + 5y)

So to factorise 27-9x+15y you need the HCM (highest common factor) of 27, 9 and 15.

HCM: 3

So you divide each of the numbers by 3 and you get

27 divided by 3 = 9

9 divided by 3 = 3

15 divided by 3 = 5

So you take the HCM (3) and then the numbers divided by it and put it into brackets

3 (9-3x+5y)