Answer:
Sarah: 18
Brother: 24
Step-by-step explanation:
The difference in ratio units is 4-3 =1. The difference in years is 6, so 1 ratio unit stands for 6 years.
Multiplying by 6, we have ...
... Sarah : Brother = 3·6 : 4·6 = 18 : 24
Sarah is 18; her brother is 24.
