Need to find How Much mL of the 85% solution is needed

Question

You need a 30% alcohol solution. On hand, you have a 385 mL of a 20% alcohol mixture. You also have 85% alcohol mixture. How much of the 85% mixture will you need to add to obtain the desired solution?

Answer 1

(385 ml)(20%) + (x ml)(85%) = (385 ml + x  ml)(30%)

7700 + 85x = 11,550 + 30x

55x = 3850

x = 70 ml of the 85% is needed.