Answer:

Explanation:
Let's recall the formula for the area of a circle:

We are given the diameter, but the formula uses the radius. Since the radius is equal to one-half of the diameter, we can find the radius by doing this:

Now that we've found the radius is 9 mm, let's substitute the values into the formula for the area of a circle. We have:

So, we've found that the exact area, in terms of pi, of either face of the coin is
.