13.6*2=27.2
7.5*2=15
10.3*2=20.6
27.2+15+20.6=62.8
2甲+2乙+2丙=62.8
甲+乙+丙=31.4
丙=31.4-27.2=4.2
甲=31.4-15=16.4
乙=31.4-20.6=10.8