There is a Building, which is tilted and equation of two different walls are $2x-y +z= 4 $ and $x+y +2z = 3.$ Angle between the walls is :

$\frac{\pi }{6}$ $\frac{\pi }{3}$ $\frac{\pi }{4}$ $\frac{\pi }{2}$

$\frac{\pi }{3}$