Please help with the bottom in red I don’t know how you get that answer

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

Which of the following expressions are equivalent ?

Nick has box brads. he uses 4 brads for the first project. nick let’s b represent the original number of brads and finds that for the second project, the number of brads he uses is 8 more than half the difference of b and 4. write an expression to represent the number of brads he uses for the second project.