The circumference of a circle is π x diameter so the length of a semicircle is (1/2)π x d. The solution to problem #2 is shown below. Let the diameters of the smaller circles be p, q, r, s. Use the formula to find the lengths of each semicircle. The same thinking is applicable to semicircle road trip problem #1.
I posted the same problem in Facebook. I asked which is longer: blue or red? More people said red.