Acertain coin is a circle with diameter 18 mm. what is the exact area of either face of the coin in term of

To find the area of the coin/a circle we use this equation:
(a = area, r = radius, d = diameter)

a = r²

So we need to do for the radius.
r = d/2
r = 18/2
r = 9

Then solve
a = 9²
a = 81

The correct answer is 81.

Hope this helped! If you have anymore questions or don't understand, please comment or DM me. :)