At a particular restaurant, each onion ring has 70 calories and each slider has 200 calories. A combination meal with onion rings and sliders is shown to have 1020 total calories and twice as many onion rings as there are sliders. Write a system of equations that could be used to determine the number of onion rings in the combination meal and the number of sliders in the combination meal. Define the variables that you use to write the system.