I need help with problem f(5) for the function f(x)=4

What is the answer to this question? i'm a bit stumped. also how do i do it? 5(x - 4) = 2(x + 5)

Which of the following will form the composite function?

The oates family went out for dinner the price of the meal was $33.95 the sales tax was 7.25% of the price of the meal . the tip was 15% of the meal and the sales tax . how much money did the oates family pay for the meal, including tax and tip