Answer
(a) $N=3.105\times A^{0.308}$
For a better visualization, see the image below.
(b) About 18 species.
Work Step by Step
(a) Using a power regression calculator we can estimate the average values and determine the equation of the power function. Using the calculator we will get the following:
$k=3.1046204 \approx 3.105$
$n=0.3080442355 \approx 0.308$
Taking these values, we will have:
$N=kA^{n}$
$N=3.105\times A^{0.308}$
(b) Using the equation calculated in (a), for $291 mi^{2}$, we will have estimated the amount of species of:
$N=3.105\times 291^{0.308} \approx 17.82135$
As the amount of species can't be non-integer, we can say that $N=18$
