(2) Solution: If X square meters are demolished and Y square meters are built, there is an equation:

x+y=7200.............( 1)

1. 1x+0.8y=7200.......(2)

(2) 0.1x-0.2y = 0 in-(1), so x=2y, 3y=7200 in (1).

∴y=2400m？ ，x=7200-2400=4800m？

That is, the original planned demolition of 4800m? The new 2400m? .

The original planned capital is 4800×80+2400×700=2064000 yuan =2064000 yuan.

The actual funds used are1.1× 4800× 80+0.8× 2400× 700 = 1766400 yuan =1766400 yuan.

Deposit 2064000- 1766400=297600 yuan.

So the green area is 297,600/200 =1488m?

(3) A main entrance and a side door can pass X and Y students on average every minute.

Then (X+2Y)*2=560.

(X+Y)*4=800

Get the door Y=80 and the door X= 120.

the second question

The total number of people in the building is 4*8*45= 1440.

The number of people who can pass through four doors in 5 minutes = (2x+2y) * 5 * (1-20%) =1600.

So it is qualified.