Hi people!

My name is John, I am beginner in this forum but could realize that you really help too much. So, I ask that you help me to solve a matter of a school work. They are 15 matters and there is one missing that I did not manage to solve. This is the question:

If F is the real function of real variable, like F(2X+1)=X for all x, so, what is the result of 2F(X)+3?