Casio Co recognizes construction revenue and expenses using the percentage of completion method. During 2016, a single long term project was begun, which continued through 2018. Information follows

2016 2017

12/31 Account Receivable 100,000 300,000

Construction expenses for year 105,000 192,000

12/31 CIP Balance 122,000 364,000

Billings during year 100,000 420,000

Profit recognize from the long term construction contract in 2017 was?

The answer is 50,000. But I don't know how we got it.