What does it mean when f(g(x)) = x ?

Tatiana reads 40 pages of her book every night for x number of nights. write an expression that shows the number of pages she has read

A)a square brown tarp has a square green patch green in the corner the side length of the tarp is (x + 8) and the side length of the patch is x what is the area of the brown part of the tarpb)a square red placemat has a gold square in the corner the side length of the gold square is (x - 2) inches with the width of the red region is 4 in what is the area of the red part of the placemat

What is 5 kilometers turned into meters