Slope of a regression line

The slope $b$ tells you how fast the predicted response rises or falls as the explanatory variable increases by one unit. A positive slope means the line goes up from left to right, and a negative slope means it goes down. For example, in $\hat{y} = 50 + 5x$ the slope 5 predicts 5 more points for each extra hour of study. It is computed as $b = r \cdot \frac{s_y}{s_x}$, where $r$ is the correlation and $s_y$ and $s_x$ are the standard deviations of $y$ and $x$.