Step 1: Time-weighted capitals (Capital $\times$ Months).
First $5$ months: all three have ₹20{,}000.
Next $7$ months (after the change):
A has ₹15{,}000; B has ₹16{,}000; C has ₹26{,}000.
Step 2: Compute each partner’s capital-months.
A: $20{,}000 \times 5 + 15{,}000 \times 7 = 100{,}000 + 105{,}000 = 205{,}000$.
B: $20{,}000 \times 5 + 16{,}000 \times 7 = 100{,}000 + 112{,}000 = 212{,}000$.
C: $20{,}000 \times 5 + 26{,}000 \times 7 = 100{,}000 + 182{,}000 = 282{,}000$.
Step 3: Ratio of profit shares and B’s amount.
Total $= 205{,}000 + 212{,}000 + 282{,}000 = 699{,}000$.
Share of B $= \dfrac{212{,}000}{699{,}000} \times ₹69{,}900
= ₹21{,}200$.
\[
\boxed{₹21{,}200}
\]