A tree breaks; the broken part forms $60^\circ$ with the ground touching at $7$ m from the base. The standing piece $h_1$ equals—

• a$7 \cdot \tan 60^\circ = 7\sqrt{3}$ m
• b$\dfrac{7}{\tan 60^\circ}$ m
• c$7 \cdot \sin 60^\circ$ m
• d$7 \cdot \cos 60^\circ$ m