Consider the following system of equations, where $\displaystyle k\in \mathbb{R}$ is an unknown constant:

x_1−x_2+x_3 = 2

3x_1+x_2− x_3 = 2

2x_1+x_2− x_3 = k

For what values of k does the system have:

(a) a unique solution

(b) infinitely many solutions

(c) no solutions

Find the solution in cases above where the solutions exist.

please explain to me how to do it ,thanks!