What must be a factor of the polynomial function f(x) graphed on the coordinate plane below?

Explanation:

The x intercepts (aka roots) are where the graph crosses or touches the x axis. These locations directly correspond to help set up the factors.

The root x = -6 shows that x+6 is a factor.

Effectively, we add 6 to both sides so that we go from x = -6 to x+6 = 0.