The shadow of a tower standing on level ground is found to be 40 m longer when the Sun's altitude is 30∘ then when it is 60∘. The height of the tower is ____.

1)h= 20$\sqrt{3}$ m
2)h= 10$\sqrt{3}$ m
3)h= 5$\sqrt{3}$ m
4)h= 30$\sqrt{3}$ m