债券的成本=1000*5%/[1000*(1-2%)]*(1-25%)=3.83%优先股的成本=500*6%/[500*(1-3%)]=6.19%普通股成本=1.2/[10*(1-4%)]+5%=17.5%加权平均成本=（1000*3.83%+6.19%*500+2500*17.5）/4000=12.67%
