Find the greatest common factor of 75, 8, and 21

Anyone know? will mark brainliest if you're correct!

[10 points, algebra 2-simplifying complex fractions]according to my answer key the restrictions are -1 and 4. but why not positive 1?

Which equation shows the variable terms isolated on one side and the constant terms isolated on the other side for the equation -1/2x+3=4-1/4x? a. -1/4x=1 b. -3/4x=1 c. 7=1/4x d. 7=3/4x