For a dataset with $n=5$ elements, the mean is $\mu = 10$ and the variance is $\sigma^2 = 6$. If we create a new dataset by $y_i = ax_i + b$ such that the new mean is $\bar{y} = 25$ and the new variance is $\sigma_y^2 = 54$, what is the value of $|a|$?