Cooper Construction Company had a contract starting April 2015, to construct a $18,000,000 building that is expected to be completed in September 2017, at an estimated cost of $16,500,000. At the end of 2015, the costs to date were $7,590,000 and the estimated total costs to complete had not changed. The progress billings during 2015 were $3,600,000 and the cash collected during 2015 was $2,400,000.

At December 31,2015 Cooper would report construction in process in the amount of?

I know that the answer is $8,280,000

I get this answer by (7,590,000+690,000)= 8,280,000 , but How do I get the 690,000?