There was some question on exam according to cost estimate.

They give you optimistic, pessimistic and most likely values.

But, they don't mention anything about PERT.

So as I know there 2 methods estimate costs.

(O+M+P)/3

and Pert

(0+4M+P)/6.

There was 2 answers one of them the sum based on Pert, another - 3 point estimates.

I've chosen (O+M+P)/3 because they don't mention Pert technique needs to be used for estimates

PMBOK says that

(0+4M+P)/6.