construction contract question

i have a series of questions and i will ask one by one agreed price of contract is 250 and estimated cost is 200 cumulative progress is as follows: year ended---------------------------2011------------------2012 costs incurred ----------------------- 80 -----------------145 work certified and billed ----------- 75 -----------------160 billings received --------------------70 -------------------150 2011 extracts based on costs incurred to date/total costs (P/L AND SOFP ARE ALSO GIVEN IN THE QUESTION AS BELOW) P/L 2011 Rev (balance) ------- 100 cost--------------------- (80) -------------------------------- profit 50x80/200)------20 QUESTION: why is Rev being calculated is a beta? since we know costs incurred, we get (80/200)x250=100. so why consider Rev as a balancing amount? SOFP 2011 EXTRACT (GIVEN) DUE FROM CUSTOMERS costs to date --------------------80 profit recognized ---------------20 billings ----------------------------(75) ------------------------------------------- -------------------------------------- 25 the question states that for 2012, the company changes from stage of completion from costs incurred/total costs to work certified/contract price and that based on this change, we are supposed to calculate the p/l and sofp for 2012 using the 4 step workings: 1. overall outcome: PROFIT/LOSS = CONTRACT PRICE - COSTS INCURRED - COSTS TO COMPLETE. since we do not know the costs to completion, this cant be done. 2. SOC = 160/250 = 64%. correct? 3. P/L: Revenue = 250x64%= 160 - rev. recognized previously=160-100=60 costs ========================== ===========145-80=(65) ---------------------------------------------------------------------------------------------- Loss ============================================(5) however, in the answer, the costs are now a balancing figure, and the profit is calculated on the basis of SOC. why? i will stop here before i ask further questions. thank u