A, B and C enter into a partnership in ratio $$\frac{7}{2}$$ : $$\frac{4}{3}$$ : $$\frac{6}{5}$$. After 4 months, A increases his share 50%. If total profit at end of one year be Rs. 21,600, n B's share in profit is:

Ratio of initial investments
$$\eqalign{ & = {\frac{7}{2}:\frac{4}{3}:\frac{6}{5}} \cr & = 105:40:36 \cr} $$
Let the initial investments be 105x, 40x and 36x
$$\left( {105x \times 4 + \frac{{150}}{{100}} \times 105x \times 8} \right)$$      $$:$$ $$\left( {40x \times 12} \right)$$   $$:$$ $$\left( {36x \times 12} \right)$$
$$\eqalign{ & = 1680x:480x:432x \cr & = 35:10:9 \cr & {\text{Hence,}}{\kern 1pt} {\text{B's}}{\kern 1pt} {\text{share}} \cr & = {\text{Rs}}{\text{.}}\left( {21600 \times \frac{{10}}{{54}}} \right) \cr & = {\text{Rs}}{\text{.}}\,4000 \cr} $$