Calculating Calamine Lotion Quantity: A Step-by-Step Guide

Let \( x \) be the amount of 60% solution needed to make 90 ml of lotion. Then, the amount of calamine in \( x \) ml of 60% solution is \( 0.60x \) ml. Since the final solution is to contain 15 ml of calamine, we have:

$$ 0.60x = 15 $$

Solving for \(x \) gives:

$$ x = \frac{15}{0.60} = 25 $$

Therefore, we need 25 ml of the 60% solution to make 90 ml of the lotion.