The zeros of the left side are x ∈ {-6, -1, 3, 7}. The product on the left changes sign at each of these values of x. The product will be positive (relation satisfied) for
x < -6 . . . . . . even number of negative factors
-1 < x < 3
7 < x . . . . . .. no negative factors (0 is also an even number)
The solution set is the union of intervals
(-∞, -6) ∪ (-1, 3) ∪ (7, ∞)
Since the relation does not include the "or equal to" case, the intervals are all open.