Given a dataset of size $n=100$ with mean $\bar{x} = 20$ and standard deviation $s = 5$. If each data point $x_i$ is transformed into $y_i = ax_i + b$ such that the new dataset has a mean $\bar{y} = 70$ and a variance $s_y^2 = 225$, which of the following is a possible pair for $(a, b)$?