Which function has a domain of all real numbers

Given f(x)= 9x+1 and g(x)=x^3, choose the expression (f*g)(x)

Sanya noticed that the temperature was falling at a steady rate of 1.4 degrees every hour from the time that she first checked her outdoor thermometer. by 6 a. m., the temperature had fallen 21 degrees. which expression can you use to find how many hours earlier she had first checked the thermometer?

Which of the following will form the composite function?