Subject: mathqa
Question: set a of 8 positive integers may have the same element and have 40 . and set b of 8 positive integers must have different elements and have 40 . when m and n are the greatest possible differences between 40 and other elements ’ sums in set a and set b , respectively , m - n = ?
Option: 
A: 25
B: 26
C: 21
D: 29
Answer: C