A sphere with the center (-2,5,3) is tangent to the plane 4x-8y+z=117. Find the radius of the sphere, the point of tangency, and the point at the other end of the diameter formed by extending the line through the center and the point of tangency.

I think I got the first part, but I don't know how to do the rest.
a) r = |(-2*4+5*-8+3*1+17)| / square root (4^2+(-8)^2+1^2)
=28/ square root (81) = 28/9