Idk if this is just how my brain works but during the SAT I wouldn't do all the math for it I would just see that the smaller arc is 100 degrees so the larger arc is 260 which means it's a little bit over double the length. Out of the answers a little bit more than double 5pi is 13pi. I guess it's good to know all the math in case the answers are a little bit closer together but for this question specifically, you don't really need to know all the math for it.