Whose agreement with whom? What are these calculations?

The phrase "Contract of whom with whom" usually relates to a legal or business context, where it is important to identify the parties of the contract — who acts as the customer, contractor, partner, etc.

As for "these calculations," without additional context, it's difficult to give a precise answer, but they typically involve financial or accounting computations related to the execution of the contract: calculating the cost of services, taxes, fines, payment schedules, etc.

In programming or business analysis, such calculations can be implemented as algorithms that consider contract conditions, deadlines, volumes, and other parameters to automate control and accounting.