A question about percentages of acid solution being added to more acid solutions. how many liters of an 80% acid solution must be mixed with a 15% acid solution to get 390L of a 70% acid solution?
I'm taking a math prep class in college and I never learned this stuff in high school. The professor wont help me

Firstly, let x = ml of 80% solution added, y = ml of 15% solution added. From there we can write down two equations.
$$\begin{eqnarray}x &+ y &= 390 \\
0.8x &+ 0.15y &= 0.70 \times 390.\end{eqnarray}$$
Are you okay to solve it from there?
