Consider the question. Jason is mixing a batch of black paint. He needs to add 2 grams of charcoal for every 30 ml of water. If he adds 900 ml of water, how much charcoal does he add?
 What is the step-by-step reasoning process to arrive at the answer: 60?
First find how many ml of water Jason needs for 1 gram of charcoal: 30 ml / 2 grams = 15 ml / g. Then divide the amount of water Jason uses by the amount of water per gram of charcoal to find how much charcoal he uses: 900 ml / 15 ml / g = 60 g.