Explanation:

- The ratio of Khushi's age to her Aunt's age is 1:4.

- The ratio of her Aunt's age to her brother's age is 9:1.

- Khushi's brother is 5 years younger than Khushi.

- Let Khushi's age be \( x \). Therefore, her Aunt's age is \( 4x \).

- Her brother's age is \( x - 5 \).

- According to the Aunt to brother age ratio, we have \(\frac{4x}{x - 5} = 9\).

- Solving the equation \(4x = 9(x - 5)\) gives \(4x = 9x - 45\). Solving for \(x\) gives \(x = 9\).

- So, Khushi is 9 years old, and her Aunt is \(4 \times 9 = 36\) years old.

- After 6 years, Khushi's Aunt will be \(36 + 6 = 42\) years old.

- The correct option is: Option 3, 42 years.

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