>>756
Acording to the supposition, x + 3y + 4z >= 16
Becouse of x, y, z is Non negative real number,4 (x + y + z) >= x + 3y + 4z
so 4 (x + y + z) >= 16
x + y + z >= 4
Since even if we divide both side by 4 which is larger than zero,
the sign of inequality is same as it was.
This above is the prove of this question
Q.E.D