vertical curve has a length of 18.75 stations. the beginning of the curve has an elevation of 476.03 feet and a station of 32 00.00. the vpi has an elevation of 498.78 feet. the end of the curve has an elevation of 481.56 feet. determine the following: a. the stations at the vpi and end of the curve. b. the grade of the back tangent in %. c. the grade of the forward tangent in %. d. the equation for the vertical curve. e. the station at the low or high point of the curve. f. the elevation at the low or high point of the curve.