How do I solve for x

What is the effect on the graph of the function f(x)=x when f(x) is replaced with -f(x)+4

I'm confused on this could anyone me and show me what i need to do to solve it.

James is playing his favorite game at the arcade. after playing the game 3 times, he has 8 tokens remaining. he initially had 20 tokens, and the game costs the same number of tokens each time. the number t of tokens james has is a function of g, the number of games he plays. write the function’s formula? t=