Formula in field

Hi,
We have a need to show a numeric figure based on the pre-fixed selection of another field, fo for example if 1000 was selected in field A, I would like field D to show “1U” on the front-end table.

I would also like to add this figure up against field B so for example:

Entry 1:
Field A: 1000
Field B: Truck One
Field D: 1U

Entry 2:
Field A: 2500
Field B: Truck One
Field D: 2.5U

If I click on Field B “Truck One” I wish to display the total of field D for a single day, which in this example is 3.5U.

Any ideas of how to begin with this? Do I need premium etc?

Many Thanks in advance.