Call the amount of pineapple "P', and the amount of gingerale "G".
We know that a mix of pineapple and gingerale makes 200 cups. So:
We also know that double the pineapple (i.e. 2P) and triple the gingerale (i.e. 3G) makes 420 cups. So:
We can now solve by substitution:
For 420 cups we need 2P=360 cups of pineapple and 3G=60 cups of gingerale]
We know that a mix of pineapple and gingerale makes 200 cups. So:
We also know that double the pineapple (i.e. 2P) and triple the gingerale (i.e. 3G) makes 420 cups. So:
We can now solve by substitution:
For 420 cups we need 2P=360 cups of pineapple and 3G=60 cups of gingerale]