It can be shown that $y_1=x^{-1},\ y_2=x^{-7}$ and $y_3=3$ are solutions to the differential equation $x^2D^3y+11 x D^2y+ 16 Dy =0$.

$W(y_1, y_2, y_3 )$ = .
For an IVP with initial conditions at $x = 8$, $c_1y_1+c_2y_2+c_3y_3$ is the general solution for x on what interval?