In some cases, the best-fitting regression equation is of the form = o + x + x + . The graph of such an equation is called a cubic. Find the least-squares regression equation for the cubic and the data given below. The equation is y = + x+ x + X Y -9 -8.3 -5 -11.5 -4 -11.3 6 8 -7 -14.4 -26 0 4 -5.7