First you need to figure out how many people one vial can accommodate. Start with 150/9 which is 16 2/3. Now you know you need to account for 80 more people. So 80-16 2/3=63 1/3 now we're at 10 vials. 63 1/3-16 2/3=46 2/3 now 11 vials repeat 46 2/3-16 2/3=30 now 13 total vials. we can estimate that 16 goes into 30 twice which totals us at 15 vials.
In order to treat 230 people 15 vials of malaria serum is needed if the estimate that 9 vials treats 150 people holds true.
