Question 3
Two $15 \,\mathrm{cm}$ rulers retain only their $3 \,\mathrm{cm}$ and $4 \,\mathrm{cm}$ marks. They overlap facing opposite directions as shown, with one ruler’s $3 \,\mathrm{cm}$ mark aligned with the other’s $4 \,\mathrm{cm}$ mark. Find the total length $L$.
