a + b + c = 72
( b : 2 ) - 2 = ( a : 2 ) - 1 + 1
( c : 2 ) - 3 = ( a : 2 ) - 1 + 2
b : 2 = a : 2 + 2
c : 2 = a : 2 + 1 + 3 = a : 2 + 4
b = 2 × ( a : 2 + 2 )
b = 2 × a : 2 + 4
b = a + 4
a + a + 4 + a + 8 = 72
a = 60 : 3 = 20
b = 20 + 4 = 24
c = 2 × ( a : 2 + 4 )
c = 2 × a : 2 + 8
c = a + 8
3 × a + 12 = 72
3a = 72 - 12 = 60
c = 20 + 8 = 28