KIndly give me a solution

A member of my family is working with a reputed coal handling plant. The person is entrusted with the responsibility of separating stones from coal in the coal yard and the transporting the stone free coals from the coal yard to the hopper. For the transportation part HYVA are used and for feeding coal in the hopper bull dozer and payloaders are used. Previously the payment was made on the basis of total working hour of the dozers, hyva and payloaders. That is payment was made against the total hour per month for each vehicle. Now the problem is, the company is saying that now the payment will be made per TON basis. That is the total quantity of coal handled in a month.

Example: If coal in the coal yard is 5000 Ton and 3000 Ton are feeded in the hopper then payment will be made for the 3000 Ton. Hence, now everyone is wondering how to relate the whole thing. i.e. how to calculate per TON rate from the working hour of the vehicles.

I hope I am able to clearly explain the question as the matter seems to be very much complicated. 

Kindly provide your suggestions.