9a−18b+21c=9, a, minus, 18, b, plus, 21, c, equals

here dude

the greatest common factor of 9, 18 and 21 is 3 so that is the number that we'll factor out

to do this divide all three numbers by 3 to get

3(3a-6b+7c)

I hope I've helped!

How are u answering so quickly .-.

im rlly smart, i have a 240 IQ

im not lying

bro you stupid

stupid

not smart