How do you do this question?

How can you solve an equation with a variable on both sides? complete the explanation. you can solve the equation by using *(blank)* operations to get the variable terms on one side of the equal sign and the constant terms on the *(blank)* side. then *(blank)* both sides by the coefficient of the resulting variable term.

Measures of the angle of r, 31 s (x+4) t (3x+9)

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