She is currently 9 years old.
If Katherine is 9, and Joel is 3, 20 years later they'll be 29 and 23. Katherine is 6 years older than him.
k = 3 j; k + 20 = 6 + (j + 20) => k = 6 + j; but k =3 j => 3*j = 6 + j => j = 3( Joel has 3 years) and k = 9 (Katherine has 9 years);
Katherine is currently 9 years old. We determined this by setting up equations based on the relationships between their ages now and in the future. By solving these equations, we found that Joel is 3 years old, making Katherine three times older at 9 years old.
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