A man invests a total sum of Rs. 10,000 in a company. A part of the sum was invested at 10% simple interest per annum and the remaining part at 15% simple interest per annum. If the total interest accrued to him in two years equals Rs. 2,400, the sum invested at 15% simple interest per annum is:
1
Rs. 8,000
2
Rs. 4,000
3
Rs. 6,000
4
Rs. 5,000