To find the sum of the distinct prime factors of 315, I need to first find all the prime factors of 315. I can do this by dividing 315 by the smallest prime numbers until I get 1. For example, I can start by dividing 315 by 3, which gives me 105. Then I can divide 105 by 3 again, which gives me 35. Then I can divide 35 by 5, which gives me 7. And finally, I can divide 7 by 7, which gives me 1. So, the prime factorization of 315 is 3^2 * 5 * 7. The distinct prime factors of 315 are 3, 5, and 7. To find their sum, I just need to add them up: 3 + 5 + 7 = 15. 
What is the sum of the distinct prime factors of 315?