I understand this but I want to be sure I’m right help me pls

What is the simplified expression for 6(2(y+x))

Let the closed interval [a , b] be the domain of function f. the domain of f(x - 3) is given by (a) the open interval (a , b) (b) the closed interval [a , b] (c) the closed interval [a - 3 , b - 3] (d) the closed interval [a + 3 , b + 3]

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