How could you find how many blocks there were in 20 stories

For f(x)=2x+3 and g(x)=x^2- 8 find (f+g) (x)

If the cost to mail a package is an initial $5 and $0.28 for every pound the total cost to mail a package was $11.27, how much did the package weigh?

What can you determine about the solutions of this system