Okay, firstly, you want to work out how many people will 1 vial of malaria treat. So, you do this:
150 divided by 9= 16.6
That means for every 1 vial, 16.6 people are treated.
Since the question asks you to find out how many vials are needed if you're required to treat 230 people, you would do this:
230 divided by 16.6= 13.8
That means you need 13.8 vials to treat 230 people.