A highway construction project is being undertaken to reduce crash rates. The reconstruction involves a major realignment of the highway such that a 65 mi/h design speed is attained. At one point on the highway, a 800 ft equal tangent crest vertical curve exists. Measurements show that at 4+50 station from PVC, the vertical curve offset is 4 ft. Assess the adequacy of this existing curve in light of the reconstruction design speed of 65 mi/h, and if the existing curve is inadequate, compute a satisfactory curve length.