Describe the surface in R represented by the equation x + y = 4. This is the set {(x, 4-x, z)|x ER, ZER} which is a horizontal plane that intersects the xy-plane in the line y = 4 - x, z = 0. This is the set {(x, 4-x, z)|x ER, ZER) which is a vertical plane that intersects the xy-plane in the line y = 4-x, z = 0. This is the set {(x, 4-x, z)|x ER, ZER) which is a vertical plane that intersects the xz-plane in the line y = 4-x, z = 0. This is the set {(x, 4-x, z)IxER, ZER) which is a horizontal plane that intersects the xz-plane in the line y = 4 - x, z = 0. This is the set {(x, y, 4-x-y)lx ER, YER) which is a vertical plane that intersects the xy-plane in the line y = 4 - x, z = 0.