Answer:
She would need 100 ml of the 8% solution
Step-by-step explanation:
You can always answer these questions using a proportion. The numerator will represent the amount of Minoxidil, and the denominator will represent the total amount of solution
She already ha 100 ml of a 4% solution. That means that she has 4 ml of Minoxidil already
We can multiply both sides by 100 for simplicity