The answer is 140.
If there are 140 hamburgers sold, and there were 2x as many cheeseburgers sold, that adds up to 420.
140 x 2 = 280 (Cheeseburgers)
So there were 280 cheeseburgers sold.
280 (Cheeseburgers) + 140 (Hamburgers) = 420 altogether.
Hope this helps!
