Sum running total

I'm needing assistance with running totals.

I'm looking to accomplish this (1):

MRN INDate Balance TotalDue

1 10-07-2017 8.00 28.00

1 10-17-2017 20.00 28.00

2 10-04-2017 20.00 80.00

2 10-07-2017 20.00 80.00

2 10-18-2017 20.00 80.00

2 10-21-2017 20.00 80.00

3 10-17-2017 50.00 50.00

Can anyone assit me as I am new and learning? Thank you /G\