i need an answer PLEASE

Question

A scientist has saline solutions with concentrations 3% and 15%. He wants to mix some of each solution to get 72 milliliters of solution with a 6% concentration. How many milliliters of each solution does he need to mix together?

Answer 1

(x ml)(3%) + (72 ml - x)(15%) = (72 ml)(6%)

3x + 1080 - 15x = 432

-12x = - 648

x = 54 mls of 3%

72 mls - 54 mls = 18 mls of 15%