Functional equation problem ( edited )

[Parishrut]

Let f : R -> R be a continuous function such that,
f(x) - 2f(x/2) + f(x/4) = x^2
then,
. f(3) = ?

Answer to be calculated in terms of f(0).

I am puzzled on how to approach such problems. Some insight would be greatly appreciated.

 

[Mark44]

Please start another new thread, showing what you have tried and using the homework template.