Dequals 9.8 mi
find the area to the nearest 10th with pi being 3.14

Assuming D is the diameter you are finding the area of a circle so the formula is A=(3.14)r

R=d/2=4.9
A=(3.14)4.9
A=15.4

A=(Pi)r^2
A is area
(Pi) is 3.14
r is radius of the circle to the second power (or squared)
Since the problem gives you diameter, you must divide that number in half to get the radius. 9.8/2=4.9

The radius is 4.9mi.

Now set up the problem.
A=(3.14)(4.9^2)
Using order of operations, solve each set of parentheses.
A=(3.14)(24.01)
Now multiply the two numbers.
A=75.3914square miles
Round to the nearest 10th.
A=75.39 square miles