Borroer_id Year Loan amount Loan maturity Loan interest
1 2011 101 60 8.5
1 2011 95 55 5.7
2 2011 85 55 8.6
3 2011 90 44 6.5
3 2012 82 46 7.5
4 2011 65 60 6.2
4 2012 67 90 5.4
5 2011 85 45 6.5
5 2011 62 78 4.5
6 2012 55 23 6.5

I would like to calculate the weighted average for the (loan amount, loan maturity, and loan interest ) according to the weight by loan amount relative to the total amount in each borrower_id.
For instance, for borrower 1, the weighted average is (101/196, 95/196), respectively equal to 0.51, 0.48 and using these percentages to calculate the weighted loan average = (101*0.51+95*0.48)=97.11
Using the same weighted average percentage created from borrower_1 loans (0.51, 0.48), I would like to use them to be applied to both the loan maturity and loan interest as well.

thank you so much in advance for your help.