Solution: If the original plan is to plant X mu of trees, plant (2400-x) mu of grass.

90% x+( 1+20%)(2400-x)= 2400

0.9x+ 1.2×2400- 1.2x = 2400

0.3x=2400×0.2

x= 1600

2400-x=2400- 1600=800

200× (1-90% )×1600-100× 800× 20% =16000 yuan.

16000 ÷ 200 = 80 (management department)

The remaining funds can also plant 80 acres of trees.