The areas of five circles were measured as 3.18 cm², 12.49 cm², 28.11 cm², 50.39 cm² and 78.42 cm²…

The areas of five circles were measured as $3.18\ \text{cm}^2$, $12.49\ \text{cm}^2$, $28.11\ \text{cm}^2$, $50.39\ \text{cm}^2$ and $78.42\ \text{cm}^2$ for the radii $1$, $2$, $3$, $4$ and $5\ \text{cm}$. Which family of function is natural? Estimate the area for $r = 7\ \text{cm}$.