6.27 Making 3D axes normal instead of boxed

Use Boxed -> False

Plot3D[2 x + 7 y, {x, -4, 4}, {y, -4, 4}, Boxed -> False, AxesEdge -> {{-1, -1}, {-1, -1}, {-1, -1}}, AxesLabel -> {x, y, z}]