x/3 = y/4 => x/15 = y/20
y/5 = z/7 => z/28 = y/20
=> x/15 = y/20 = z/28
=> 2x/30 = 3y/60 = z/28
Áp dụng..
2x/30 = 3y/60 = z/28 = 2x + 3y - z /30+60-28 = 186/62 = 3
2x = 3 . 30 = 90 => x = 45
3y = 3 . 60 = 180 => y = 60
z = 3 . 28 = 84