a + b = 12561
b + c = 16599
a + c = 21226
a + b + b + c = 12561 + 16599
a + 2 × b + c = 29160
21226 + 2 × b = 29160
2 × b = 29160 - 21226
2 × b = 7934
b = 7934 : 2
b = 3967
a = 12561 - b
a = 12561 - 3967
a = 8594
c = 21226 - a
c = 21226 - 8594
c = 12632