С1=m/(60+m)
C2=m/(80+m)
C1:100
C2:95
C2=C1×0.95
m/(80+m)=m/(60+m)×0.95
60+m=(80+m)×0.95
60+m=76+0.95m
0.5m=16
m=32
Ответ: 32 грамма