Answer:Gary-18 years brother-10 years
Step-by-step explanation:1st case: brother=1 yrs,gary=3 yrs=>after 6 after: brother =7 yrs gary=9 years
2nd case:......
3rd case:.....
4th case:brother:4 years gary:12 yrs=>after 6 yrs:brother=10 yrs gary=18 yrs=>18-10=8