A US dime has a diameter of 18 millimeters. That makes the radius 9 millimeters, because
[tex]\begin{gathered} \text{radius}=\frac{\text{diameter}}{2} \\ \text{radius}=\frac{18}{2} \\ radius=9 \end{gathered}[/tex]The area of the dime (which is circular in shape) is given by the formula;
[tex]\begin{gathered} \text{Area of a circle} \\ A=\pi\times r^2 \\ r=9,\pi=3.14 \\ A=3.14\times9^2 \\ A=254.34mm^2 \end{gathered}[/tex]The area of one side of the dime is 254 square millimeters (approximated to the nearest square millimeter)