what is the area, in square centimeters, of a circle with a diameter of 14 centimeters?
Area of a circle is given by $${\frac{{\mathtt{\pi}}{\mathtt{\,\times\,}}{{\mathtt{diameter}}}^{{\mathtt{2}}}}{{\mathtt{4}}}}$$
You can plug your numbers into this formula using the calculator on the home page of this site.
http://web2.0calc.com/formulary/math/geometry/circle