Should the independent variable be placed on the x axis or the axis

For f(x)=2x+1 and g(x)= x^2 -7, find (f•g)(x)

Julie goes to the sports store and spends $40.50 before tax. she buys a pair of shorts for $21.75 and 3 pairs of socks that each cost the same amount. how much does each pair of socks cost? $$

You are riding your bike and notice the square sign above. you mentally draw a straight line from point a to c. describe the angle relationship between dca and bca