Use traces to sketch the surface. (If an answer does not exist, enter DNE. Select Update Graph to see your response plotted on the screen. Select the Submit button to grade your response.) 7x2 + 6y2 + z = 0 (Write an equation for the cross section at z = 5 using x and y.) (Write an equation for the cross section at z = 5 using x and y.) (Write an equation for the cross section at y = 0 using x and z.) (Write an equation for the cross section at x = 0 using y and z.)