a/15 = (b+2)/12 = (c+13)/18
12a=15b+30 a=(15b+30)/12
18b+36=12c+156 c=(18b-120)/12
18a=15c+195
(a+b+c)/3=95
a+b+c=285
(15b+30)/12+b+(18b-120)/12=285
15b+30+12b+18b-120=3420
45b=3510
b=78
a=(15b+30)/12 =(15*78+30)/12=100
c=(18b-120)/12=(18*78-120)/12=107
a=100
b=78
c=107