Nickel has a face$-$centered cubic crystal structure. The possible slip directions at $(111)$ slip plane in nickel are $[01-1],[10-1]$ and $[1-10].$ A single$-$crystal nickel is under tensile test along $[110]$ direction. Answer the following questions:

Find the slip direction along which the shear stress at $(111)$ plane is not zero.

Determine the tensile stress at which the yielding begins if the critical shear stress is $12$MPa.