To solve this question we will use the following diagram:
Notice that the area of the shaded region is the area of the rectangle with length 14 and width 7 minus 2 times a quarter of the area of a circle with radius 7, meaning:
[tex]SA=14\times7-2(\frac{\pi\times7^2}{4}).[/tex]
Reducing the above expression we get:
[tex]\begin{gathered} SA=98-\frac{\pi\times49}{2}, \\ SA\approx21.03. \end{gathered}[/tex]
Answer: The best estimation of the area of the shaded region is option A) 21.
