(b) (10pts) A parametric surface S is given by r = 4u'+v, y = 2u+ 0, 2 = UV, (u, V) ER. Find all the points (To, yo, 20) on the surface S where the tangent plane of S at (To, yo, 20) is horizontal (i.e., parallel the ry-plane). Note that you can first find all the parameters (uo, vo) such that the tangent plane at r(up, vo) is parallel to the xy-plane. Then the points in R are given by (Co. yo, 20) = r(un; Vo)