x+y=11k
x+z=14k
y+z=15k
x+y+x+z+y+z=11k+14k+15k=40k
2(x+y+z)=40k
x+y+z=20k
x=20k-15k=5k
y=20k-14k=6k
z=20k-11k=9k
(2xy-xz)/x+3y-z)=15/7
(2×5k×6k-5k×9k)/(5k+3×6k-9k)=15/7
(60k²-45k²)/(5k+18k-9k)=15/7
15k²/14k=15/7
k/14=1/7
k=14/7=2
x=5k=5×2=10
y=6k=6×2=12
z=9k=9×2=18
