We will need to rearrange the equations into the form y = mx + c, where m and c are some real numbers. In such a form, m will be the slope.
2x + y = 8
y = -2x + 8
y = (-2)x + 8
Thus, the slope in this case is -2.
x - y = 4
y = x - 4
y = (1)x - 4
Thus, the slope in this case is 1.