Final answer:
B would have joined A for business after 3 months. Therefore, the correct option is C.
Step-by-step explanation:
To calculate the months after which B would have joined A for business, we need to compare the initial investments of A and B. A started with ₹ 45,000 and B joined later with ₹ 30,000.
The ratio of their investments is 45,000:30,000, which simplifies to 3:2.
Since the ratio of their profits at the end of one year is 2:1, it means that B would have joined A for business after 3 months.