Write a user-defined function that calculates grade point average (GPA) on a scale of 0 to 4, where A = 4 B = 3 C = 2 D = 1 E = 0 and . For the function name and arguments use av = GPA(g,h). The input argument g is a vector whose elements are letter grades A, B, C, D, or E entered as strings. The input argument h is a vector with the corresponding credit hours. The output argument av is the calculated GPA.