A wind tunnel has a 1-m2, 6-m-long test section in which air at standard sea-level conditions moves at 70 m/s. It is planned to let the walls diverge slightly (slant outward) to compensate for the growth in boundary-layer displacement thickness, and thus maintain a constant area for the inviscid flow. This allows the free-stream velocity to remain constant. At what angle should the walls diverge to maintain a constant velocity between x = 1.5 m and x = 6 m?