In an experiment, two liquids with different viscosities (thickness) are allowed to drip a drop at a time into a flask, where they are mixed. The apparatus is set up such that the first liquid drips 3 v ^3 − 2 v + 20 milliliters per minute and the second liquid drips v + 2 milliliters per minute, where v is the average viscosity of the final mixture. Which equation shows how many milliliters of the first liquid are mixed for every milliliter of the second liquid?