To find the area of a circle, you can use the formula:
\[ \text{Area} = \pi r^2 \]
where \( r \) is the radius of the circle. The radius is half of the diameter. Given a diameter of 10 millimeters, the radius \( r \) can be calculated as:
\[ r = \frac{\text{diameter}}{2} = \frac{10 , \text{mm}}{2} = 5 , \text{mm} \]
Now, use the value of \( \pi \) as 3.14 to calculate the area:
\[ \text{Area} = 3.14 \times (5 , \text{mm})^2 \]
Calculating \( (5 , \text{mm})^2 \):
\[ (5 , \text{mm})^2 = 25 , \text{mm}^2 \]
Now substitute that into the area formula:
\[ \text{Area} = 3.14 \times 25 , \text{mm}^2 \]
Calculating that product:
\[ \text{Area} = 78.5 , \text{mm}^2 \]
Therefore, the area of the circle is approximately \( 78.5 \) square millimeters, rounded to the tenths place.
The correct answer is:
78.5 square mm.