Explanation

The EOQ formula is $\sqrt{\frac{2 \cdot D ext{ (annual demand)} \cdot S ext{ (ordering cost)}}{H ext{ (holding cost)}}}$. If $D$ triples and $S$ reduces by 3, the new EOQ will be proportional to $\sqrt{3 \cdot (1/3)}$, which is $\sqrt{1}$, meaning it remains unchanged.