Description for Correct answer:
Given,

2x + 3y + z = 55 ....(i)

x + z - y = 4 ...(ii)

y - x + z = 12 ...(iii)

From (ii) and (iii)

2z = 16 => z = 8

From (ii), x + 8 - y = 4

=> x = 4 - 8 + y = y - 4

Putting this value in (i) we get

2 (y - 4) + 3y + 8 = 55

=> 2y - 8 + 3y + 8 = 55

=> 5y = 55 => y = 11