A scatter plot of $n=20$ points has a mean of $x$ values $\bar{x} = 5$ and mean of $y$ values $\bar{y} = 10$. The sum of products $\sum (x_i - \bar{x})(y_i - \bar{y}) = 150$. If the variance of $x$ is $25$, what is the slope $b_1$ of the regression line $\hat{y} = b_0 + b_1x$?