Two circles and a rectangle overlap in the figure. What is the sum of the numbers that lie inside the rectangle and inside exactly one of the two circles?

Inside the rectangle and in just one circle: 4 (left circle) and 9 (right circle), so the sum is 13. 16 adds the 3 that is in both circles, 26 takes every number in the rectangle, and 23 adds the rectangle-only 10.