Reason: △AOD is similar to △BOC because of AD‖BC, and the value of DO/OB is 5:8 (area ratio = similarity ratio square) because the area of △AOD is 25 and the area of △BOC is 64.
Because the value of DO/OB is 5:8, the value of AO/CO is 5:8, and because the area of △BOC is 64, the area of △AOB is 40 (△AOB: △ BOC = 5: 8 is the same height, and the value of △ AOB is 40).