The quadratic equation is: 
 and the two values of
 and the two values of 
 will be 40 and 60 that will create a profit of $600.
 will be 40 and 60 that will create a profit of $600. 
Step-by-step explanation
The cost function is: 
 and
 and 
The revenue function is: 

As the profit means 
 , so the Profit function will be....
, so the Profit function will be....

So, the quadratic equation is: 

Now for creating a profit of $600 means, we will plug 
 into the above equation. So.....
 into the above equation. So.....

Now applying zero-product property.....

So, the two values of 
 will be 40 and 60 that will create a profit of $600.
 will be 40 and 60 that will create a profit of $600.