c = ilosc osob nalezacych do partii Cymbalkow
t = ilosc osob nalezacych do partii Trabek
c - 4 = t + 4
c + 4 = 3 ( t - 4 )
c = t + 8
t + 12 = 3t - 12
c = t + 8
t + 24 = 3t
c = t + 8
24 = 2t
c = t + 8
t = 12
c = 20
t = 12
odp: do partii Trabek nalezy 12 osob.