1) Find the normals to the planes: <4,1,-4> and <1,0,8>
2) These can lie in the perpendicular plane, so the cross product of the normal vectors is the normal of the intersecting plane.
Find the the determinant of rows i,j,k ,<4,1,4>, and <1,0,8> = normal to plane (cross product)
3) The equation of a plane given its normal and a point on the plane if we take the normal to be <n1,n2,n3> and the point is (xp, yp, zp)
n1(x - xp) + n2(y - yp) + n3(z-zp) = 0