Hello all, I am trying to implement google spreadsheet in a project, I need your help if you have knowledge about it

The spreadsheet I will collect from students will look like this, I need formula which will calculate the workload automatically, if the workload is as below

Work load

Chemistry I = 6      physics I = 7     Biology I = 5

Chemistry II = 8    Physics II = 8     Biology II = 6

Chemistry III = 9  Physics III = 10     Biology III =8

What I am trying to achieve is that I will send google forms and student will response me back on what classes they are taking this semester. It will be saved into my google spreadsheet automatically once they submit the form. I want to give work load number of each subject as above. How do spreadsheet or excel can automatically calculate the workload above? What kind of logic should it use? I was thinking something like below

First give value to each subject of column A

If column A = chemistry I, value = 6, if column A = chemistry II, value = 8 ……… if column B = physics I, value = 7 …………., If column C = Biology I, value = ……. And so on

whenever a student submit the google form, then add values of column A , column B and  column C and put it in column D. 

I know it might be doable, but I don’t have any experience

using logical formulas on spreadsheets, any ideas friends? It will mean a lot to me, thanks in advance