F₁ = 10 H
F₂ = 180 H $$\displaystyle \frac{F_{2} }{F_{1}}= \frac{S_{2}}{S_{1}}=> \\ S_{1}= \frac{F_{1}S_{2}}{F_{2}}$$
S₂ = 90 см²
--------------- $$\displaystyle S_{1}= \frac{10*90}{180}=5(см²)$$
S₁ = ?

Ответ: 5 см²