I think it is D:{5,-infinity}
120 - 3/4y=60
lowest common multiple=4y
480y-3=240y
480y-240y=3
240y=3
y=3/240
y=1/80
Answer: y=1/80
If we want to know the greatest common factor, we should ask: is one of the numbers divisible by the other? if yes, then the smaller number will be the answer!
let's try:

so, yes!
6 is the greatest common factor of the two:)