Consider the question. Carla is making smoothies. If she uses 500 ml of watermelon puree and 100 ml of cream, how many 150 ml servings can she make?
 If the answer is '4'; explain the reasoning:
First find the total volume of the smoothie mix: 500 ml + 100 ml = 600 ml. Then divide the total volume by the volume per serving to find the number of servings: 600 ml / 150 ml / serving = 4 servings.