Answer:
Kate's age is 6. Marcia's age is 18.
Step-by-step explanation:
Let Kate's's age = k
Marcia is 3 times older, so Marcia's age is 3k.
The difference in ages is 3k - k.
We are told the difference in ages is 12, so
3k - k = 12
2k = 12
k = 6
Kate's age is 6.
3k = 3(6) = 18
Marcia's age is 18.