For first 9 months, A and B invested INR90,000 and INR60,000. Their investment did not change for next 3 months.
For first 9 months, C invested INR0. Next 3 months, C invested INR90,000.
Investment ratio of A, B, C in that year is 270,000:180,000:90,000 -- 27:18:9 --- 3:2:1
C's share in the profit is 1/6(total proft) = 15,000
Total profit = INR90,000
B's share in the profit = 2/6(total profit) = 1/3(90,000) = INR30,000
10% of the B's profit goes to charity so it is = 10/100*(30,000) = INR3,000
Money donated to charity by B = INR3,000