What is the greatest common factor of 8 and 36

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

Solve each quadratic equation by factoring and using the zero product property. x^2 - 8x + 30 = 3x

The area of a rectangle is 10 cm^2. one side of the rectangle is x cm. express the perimeter of the rectangle in terms of x and show that this rectangle cannot have a perimeter of 12 cm. the perimeter of the rectangle in terms of x is __ cm