The slope of the line passing through the points (2, -1) and (x, 5) is -1. Find x?

$$\eqalign{ & {\text{Slope}} \Rightarrow m = - 1 \cr & m = \frac{{{y_2} - {y_1}}}{{{x_2} - {x_1}}} \cr & - 1 = \frac{{5 - \left( { - 1} \right)}}{{x - 2}} \cr & - 1\left( {x - 2} \right) = 6 \cr & - x + 2 = 6 \cr & x = 2 - 6 \cr & x = - 4 \cr} $$