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 50×80/200)——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 = 250×64%= 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