Claude Ebair has hired a team of chemists to create the world's longest lasting perfume, which he plans to cal 24/7. On their first attempt, the chemists combined 5 milliliters of a substance containing 2% sandalwood with another substance containing 6% sandalwood to get a substance containing 5% sandalwood. How many milliliters of the substance containing 6% sandalwood must the chemists have used?