2.5 × 10⁻⁹ × 1.5 × 10³ = 3.75 × 10⁻⁶
as you can see, you multiply the numbers in front of 10s, and add the exponents.
i can .
the equation for area of a circle is a=πr*2
if your diameter is 13 simply take half of that and plug into the equation
π(6.5)*2 which when put into a calculator comes out to 132.732289
based on their bhavior