Angular Finding Student Results

I am trying to create student information system. I am working with Angular 7 and new to it.

Image showing how my results will be in stumarks.html

I get my data from json in the below format.

{
"regno":"1001",
"name":"Arun",
"marks":"76"
}

Now I want to calculate present, absent, fail class average etc. Can anyone help me in creating the typescript code for stumarks.component.ts and stumarks.html

Note**: AB- Means absent and should be excluded from total students present. Fail means students marks below 50 and Class Average = Total marks of all present students/ Total students present