The formula to find the circumference of a circle given the information we know (the diameter), you could use the circumference formula of c=pi*diameter or: c=3.14 * 4 c=12.56 is the circumference IF THE CIRCLE WAS WHOLE, but since we're working with a semicircle (and in this case, what looks to be exactly 1/2 of a circle), you could divide 12.56 by 2 and come up with 6.28 as the circumference of each of the semicircles.
(Excel works great with this and will solve it for you, use the PMT function and insert the numbers provided. It will show a (-) but that is because a positive PV is placed.)
