Alcohol mixing problem

Question

You need a 35% alcohol solution. On hand, you have a 140 mL of a 20% alcohol mixture. You also have 45% alcohol mixture. How much of the 45% mixture will you need to add to obtain the desired solution?

Answer 1

Let x = number of mL of the 45% solution

Then 0.20(140) + 0.45x = 0.35(x + 140)

Solve for x!