How do you find the greatest common factor of ##140n, 140m^2, 80m^2##?

Factorize. But you can see at a glance that the letters have no common factor.

So we're left with finding the GCF of ##140,140,80##

##140=7xx20and 80=4xx20##

So the GCF ##=20## (no common factors between ##4## and ##7##)

Note: Of course you could factorize all the way down to the primes:

##140n=2xx2xx5xx7xxn##, etc.