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.