A box of strawberries, containing $12$ strawberries total, costs $2$. A box of blueberries, containing $48$ blueberries total, costs $3$. Suppose that for $12$, Sareen can either buy $m$ strawberries total or $n$ blueberries total. Find $n - m$.

Let's think step by step and output the final answer within \boxed{}.
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