Answer:
Draw a Venn diagram with the left circle labeled brother, and the right labeled sister. Label the middle both and fhe outisde neither. Put 5 in brother, 3 in sister, 6 in both and 6 in neithrr.
Step-by-step explanation:
11+9 = 20
20-6 = 14
20-14=6
There are 6 that have both
