Question about payments

Hello, I have 2 farms. One farm has 4 workers, the other has 3 workers.
The farm with 3 workers on the Billing tab says the following: 666

According to my calculations, the following appears:

3 RIG * 0.29(Daily cost) = 0,87$ full Daily cost

How do you get this $3 price?

Can I have a little explanation?

I am still waiting for an answer to my question.