Let X - 8 d 8 - X mean that X - 8 has the same distribution as 8 - X; thus X has a symmetric distribution about 8. Say that Y and X are independent random variables and Y has a distribution which is also symmetric about 8. Show that X - Y has a distribution that is symmetric about zero.
Hint: Write X - Y = X - 8 - ( Y - 8) d 8 - X - (8 - Y) = Y - X.