Two wires are made of the same material and have the same volume. The first wire has a cross-sectional area A and the second wire has a cross-sectional area 3A. If the length of the first wire is increased by $∆\mathrm{l}$ on applying a force F, how much force is needed to stretch the second wire by the same amount?

1. 9F

2. 6F

3. 4F

4. F