When manufacturing the fuselage of a commuter airplane, aluminum plates are adhesively bonded together with lap joints. Because the elastic deformation for a single plate differs from the deformation for two plates in a lap joint, the maxim um shear stress in the adhesive is twice as high as the average shear stress. The shear strength of the adhesive is 20 M Pa, the tensile strength of the aluminum plates is 95 M Pa, and their thickness is 4.0 mm . Calculate the overlapping length needed to make the adhesive joint twice as strong as the aluminum plate.