Zakaat of Partners with a Joint Debt

Three partners (all Muslim A, B, C) start a used car business. All three invest an amount of R 450 000-00 each. Total therefore is R 1 350 000-00. All partners share equally in profits.

The stock on hand as at 27 Ramadhaan = R 1 800 000-00. The surplus of R 450 000-00 is drawn from an acess bond of person A.
Please advise on how to calculate the Zakaat considering that:
Person A input = R450 000 & balance = R450 000
Person B input = R450 000 & balance = R450 000
Person C input = R450 000 & balance = R600 000
The reason for this is that person A & B are drawing the profits out and living of the same. However, person C has re invested his profit in the business, thus having a balance of R600 000.
How do we work out the Zakaat for A,B,C considering that R450 000 is still owing to the bank.