Revenue Example 5 open tution

Dear tutor,

In example 5 performance obligations ober time and the statement of profit and loss. We have the following data.

Alex commenced a three year building contract during the year ended December 2014 and continued the contract during 2015. The details of the contracts are as follows

Total contract value. 45m
Costs incurred to date 2015. 20
Estimated costs to completion. 12
Work certified as completed in 2015. 15
Stage of completion at 2015. 70%
profit recognised to date 2014. 3.3

The solutions:

Revenue. 15
Cost. (9.2)
Profit (9.1(w)-3.3 5.8

How was the cost calculated at 9.2 for the year?

Thank you in advance.