Function If and or with multiple statement

pleese help me. I have problem given the details of the weight of the course values ​​as follows:

value   weight
A         4
B         3
C         2
D         1
E         0

known formula to calculate student achievement index is : enter image description here

by n stating the number of courses that have been taken by the student. a. create a function program to calculate a student's achievement index based on the weight and formula details. Write the syntax of the program. (hint: program input is the credits column of the course and the value column) b. by using the program you have created, calculate the achievement index of a student who has details of the following values:

the name of the course     sks     value
P                           3        C
Q                           2        A
X                           2        B
Y                           3        C
Z                           2        B