You work in a pharmacy that mixes different concentrations of saline solutions for its customers. The pharmacy has a supply of two concentrations, 0.50% and 2%. The function y = 100(0.02) + x(0.005) / 100+x gives the amount x in milliliters of the 0.5% solution you must add to 100 milliliters of the 2% solution to form a new concentration y of saline solution. How many milliliters of the 0.5% solution must you add for the combined solution to have a concentration of 0.78%

You must add approximately (answer) mL.
(round to one decimal as needed).