You can use GeoGebra to find the revenue function and the demand. 
If you want to find the revenue function when you have the price function , go to Item 3.
If you want to find the demand that yields the greatest profit, and also use it to find the greatest revenue and the price of the product, go to Item 3.
If you want to find the demand when you have the revenue function , go to Item 3.
     GeoGebra Instruction 1
Algebra     View     under         View     in         Menu.         Algebra View, like this:         p(x) = <Expression>
where you replace <Expression> with your expression. Press Enter.         
Algebra View, type         R(x) = Expand(x * p(x))
Press Enter. Your revenue function                  is displayed in the same row. 
     GeoGebra Instruction 2
GeoGebra.         Extremum(<Polynomial>)
where you replace <Polynomial> with R. The         -coordinate         of the point you get is the demand that yields the greatest revenue, while the         -coordinate         is the greatest revenue itself.         
p(e)
where e is replaced by the value of the         -coordinate         from the previous step. The value you get is the price that yields the greatest         revenue. You can also type  
(p, e(p))
which gives you a point on the graph of showing the price along with the point from the previous step.
      
     GeoGebra Instruction 3
If you have followed the instructions above, it’s recommended that you save the GeoGebra file you were working with now, close it, and open a new GeoGebra file.         
CAS     under         View     in         Menu.         R(x) := <Expression>
in CAS, where you replace <Expression> with your expression. Don’t forget the         colon before the equals sign!         
Solve(<Equation>, <Variable>)
where
<Equation>         is               replaced               with               p         =         R/x,               
<Variable>         is               replaced               with               x. 
GeoGebra will print an equation        The right-hand side of this equation is the demand.