就是76.
A+B+C+D+E=5×91.9A+B+C＝3×88C+D+E＝3×90.5C=(A+B+C)+(C+D+E)-(A+B+C+D+E)
1式:A+B+C+D+E=91.9*4=367.62式:A+B+C=88*3=2643式:C+D+E=90.5*3=271.5用3式+2式=A+B+2C+D+E=535.5(式4)将式4-式1,得:C=76
