If a polynomial function has roots -8,1 and 6i what must also be a root of f(x)

When the solutions to each of the two equations below are graphed in the xy-coordinate plane, the graphs of the solutions intersect at two places. write the y-cordninates of the points of intersection in the boxes below in order from smallest to largest. y=2x y=x^2-3

Ineed with math stuff it involves graphs

How can you find the mean absolute deviation (mad) for this set of data?