1/(x+y)=40
1/(y+z)=35
1/(x+z)=56
x+y=1/40
y+z=1/35
x+z=1/56
2(x+y+z)=1/40+1/56+1/35
2(x+y+z)=(7+5+8)//5*8*7=1/14
1/(x+y+z)=28
ответ за 28 минут
