Answer
S = 2.69 x $10^{1}$ $cm^{2}$ is the difference between the surface of two circles.
Work Step by Step
First we have to find the surface of each circle and than find the difference in surface.
For circle with radius 7.98 cm:
$S_{1}$ = $π\times{r}^{2}$
$S_{1}$= $3.14\times({7.98 cm})^{2}$
$S_{1}$= 199.956 $cm^{2}$
For circle with radius 8.5 cm:
$S_{2}$ = $π\times{r}^{2}$
$S_{2}$= $3.14\times({8.5 cm})^{2}$
$S_{2}$= 226.865 $cm^{2}$
The difference: S =$S_{2}$ - $S_{1}$
S = 226.865 $cm^{2}$ - 199.956 $cm^{2}$
S = 26.908 $cm^{2}$
S = 26.9 $cm^{2}$ ( to three significant figures) or
S = 2.69 x $10^{1}$ $cm^{2}$
