ow ow ow ow For the functions w = xy + yz + xz, x= 3u + v, y = 3u -v, and z = uv, express a and using the chain rule and by expressing w directly in terms of u and v before differentiating. Then evaluate , and at the point (u, v) = -7-1 ow ow Express - and as functions of u and v. ow du aw av ow ow Evaluate au and at (- 4 -1) au - 1) "Type an integer or a simplified fraction.) av (Type an integer or a simplified fraction.)