A vertical curve with grade1= 3.6% meets the exit grade of -4.7% at PVI located at station 26.50. A vertical curve of 700 feet is propsed to provide the transition between the two grades. What is the offset at the midpoint on the curve ( elevation difference between PVI and midpoint on the curve). Assume the nearest bench mark is located at station 25.00 with an elevation of 525.00 feet.