So since both these lines are solid lines and not dashed lines, the inequality is going to be either ≥ or ≤.
Starting with the horizontal line, all the points on that line have the y-coordinate of 6, therefore this line is going to be y_6. And since the shaded region is below the line, this inequality is going to be y ≤ 6.
With the next line, it is y_x. The y-intercept is (0,0) and the slope is 1. And since the shaded region is above this line, this inequality is going to be y ≥ x.
In short, the system of inequalities is y ≥ x and y ≤ 6.