We are given that 
.
Substitute x with 5-x, then the above equation becomes:
, that is
So, we have the following system of equations:
i)
ii)
multiply the first equation by -4, so that we eliminate f(5-x)'s
i)
ii)
adding the 2 equations side by side we have:
expanding the binomial, and collecting same terms we have:
dividing by -5:
dividing by 3:
Answer:
Substitute x with 5-x, then the above equation becomes:
So, we have the following system of equations:
i)
ii)
multiply the first equation by -4, so that we eliminate f(5-x)'s
i)
ii)
adding the 2 equations side by side we have:
expanding the binomial, and collecting same terms we have:
dividing by -5:
dividing by 3:
Answer: