Six plus eight eqauls ??

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

If f(x) = 4 - x2 and g(x) = 6x, which expression is equivalent to (g-f)(3)? 06-3-(4 + 3)2 06-3-(4-33 6(3) - 4 +32 6(3) -4 -32

Solve the following pair of equations for x and y: ax/b_ by /a= a +b; ax - by = 2ab