求abc的值.a+b+c=33,a+a+b=31,a+b-c=9该怎么做?

b = 31 - 2a
31-a+c=33 -> c-a=2
31-a-c=9 -> a+c=22
-> c = 12
a = 10
b = 11
abc = 10*11*12 = 1320
a+b=35.2
a-b=25.8
->2a=61 -> a=30.5
->b=4.7
ab = 143.35