Math! anyone know this algebra 2 question?

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

Which expression is equal to (21)(7)(3x) using the associative property? (21 · 7 · 3)x (7)(21)(3x) 32(7 + 3x) (3x)(7)(21)

The area of the map is the product of the length and width. write and expression for the area as the product of the two binomials do not multiply