number of the day number 7 and 15

if your diameter is 6 then plug in 3.14 x 6. this will equal 18.84.

following the first example with the diameter being 6, you can calculate the radius and use that as well. the radius equals 1/2 of the diameter so radius equals 6 divided by 2. that equals 3. now you can plug 3 into the formula 2(3.14) x 3 which also equals 18.84.