3) Waterline length =(20+ 10)×2=60m.

4) Water injection: 20× 10× 1.5=300m?

4. Purchase price = 1040÷ 130%=800 yuan;

* * * Profit:

( 1040-40-800)×40×90%-800- 1040×0.6×40

×( 1-90%)

=7200-704

=6496 yuan