An existing equal$-$tangent sag vertical curve is designed for $50$ mph$.$ The initial grade is $-3\%$

and the elevation of the PVT is $750$ ft$.$ The PVC of the curve is at station $136+00,$ and the PVI

is at $139+28.$ An overpass is being constructed directly above the PVI. The highway is for

cars and combination trucks. What is the lowest possible elevation of the bottom of the

overpass structure to ensure sufficient stopping sight distance at $50$ mph$?$ If you need a K

value corresponding to the design speed, use the table from Problem $3.$