The illustration above shows the item needed for an investigation. which item is the independent variable? which items are the constants? what might a dependent variable be?
The independent variable are the pots that you use (different thing same method)
A possible dependent variable is the tomatoes, the amount of time you cook them (assuming thats what you're supposed to do) the temperature, etc, what you need to keep the same.
I'm unsure of the constants though, sorry. Hope this helped a bit!