X+y+z=91

x:9=2:5 → 5x=18 → x=3.6

y:z=5:6 → 6y=5z →y=5z:6

3.6+5z:6+z=91

11z:6=87.4 → z=47.672

y=5*47.672:6=39.727

Ответ

x=3.6

y=39.727

z=47.672