1. The minimum compensation for the excess part is 8260-400=7860 yuan.

Need to pay 7860*( 1-45%)=4323 yuan.

2. Let the original number of girls be X. Since the number of boys has not changed, the number of boys is x/5*6, which is also equal to (x+5)/8/9, that is, x/5*6=(x+5)/8/9 and x=75.