Need help for upcoming exam!

I’ve got a math exam in a couple weeks regarding: - Functions (Linear & Exponential) - Probabilities - Interpreting graphs of functions - Equations, both with functions or algebraic.

This might seem like child’s play for most of you but I’m quite young and need tips to study these topics for the exam! I already have a basic grasp on functions and know probabilities very well. However the problems I get stuck on the most are questions like these (Taken from a practice exam):

Following is true for a function f where f(x) = kx + m - f(x + 4) + f(-x) = 15 - f(2) = 5m

Determine function f: ???

I just can’t wrap my head around these questions and would appreciate any advice on how to solve them! Thank you!

Edit: Grammar