Let $W(s,t) = F(u(s,t), v(s,t))$ where $$u(1,0) = 8, u_s(1,0) = 7, u_t(1,0) = 8$$ $$v(1,0) = -7, v_s(1,0) = -2, v_t(1,0) = 4$$ $$F_u(8, -7) = 7, F_v(8, -7) = 5$$
$W_s(1,0) =$ $W_t(1,0) =$