Start from a baseline where the entire Rs. 25,400 is imagined to sit in Scheme Y at 10% for 2 years. This baseline interest would be \[ 25400\times\frac{10}{100}\times2=5080. \] The actual interest earned is Rs. 6,460, which is \[ 6460-5080=1380 \] more than this baseline. Every rupee that actually sits in Scheme X instead of Y earns the higher 18% rate rather than 10%, a difference of 8% per annum, or \( 8\times2=16\% \) over the full 2 years. So the amount of money actually sitting in Scheme X is whatever amount, at this extra 16% over 2 years, produces the additional Rs. 1,380: \[ \text{Amount in X}=\frac{1380}{16\%}=\frac{1380}{0.16}=8625. \] The amount in Scheme Y is then the remainder, \( 25400-8625=16775 \). Test each option as the amount in Scheme Y under this baseline-and-shift reasoning.
Measuring how much extra interest the actual mix earns above an all-Scheme-Y baseline shows exactly Rs. 8,625 must sit in Scheme X, leaving Rs. 16,775 in Scheme Y.
Therefore, the correct answer is Rs. 16,775.