Formula help
posted by David .
Let f(x) = 1/(x+7)+15/(x8). Find all a for which f(a)=f(a+15).
How do I solve this problem?

ok, solve.
f(a)=f(a+15)
1/(7+a) + 15/(a8) = 1/(a+22) + 15/(a+7)
multiply both sides of the equation by
(a+7)(a8)(a+22)
and solve. 
This is a multiple choice question and I am not getting any of the choices
a.) 161/8
b.) 120/7
c.) 161/7
d.) 17 
Nor do I.