A prime contractor in a customer project under CPFF contract has run into unexpected technical problems. Fixing them will require a lot of additional work to be done.

The company made a decision to book more staff and equipment from their subcontractors in order to adhere to the agreed timeline. The customer agreed to this decision.

What will most likely happen?
 
A)       The contractor‘s indirect costs will increase and the customer‘s payment for them will increase, too.
B)        The contractor‘s indirect costs will increase, but the customer‘s payment for them will not increase.
C)        The contractor‘s indirect costs will not increase, but the customer‘s payment for them will.
D)        Both the contractor's indirect costs and the customer‘s payment for them will not increase.

I thought that costs would increase on both side because more staff needs to be paid as well as equipment... but that's wrong. Why?