A man received Rs. 12000 as Puja Bonus. He invested a part of it at 5% per annum and the remaining at 6% per annum, simple interest being allowed in each case. The total interest earned by him in 4 years is Rs. 2580. The sum invested at 5% per annum is

Let sum invested at 5% be Rs. $$100x$$ and sum invested at 6% be Rs. $$(12000-100x)$$ and time period = 4 years

Simple interest = $$\frac{P\times R\times T}{100}$$

According to ques,

=> $$(\frac{100x\times5\times4}{100})+(\frac{(12000-100x)\times6\times4}{100})=2580$$

=> $$20x+24(120-x)=2580$$

=> $$20x-24x+2880=2580$$

=> $$4x=300$$

=> $$x=\frac{300}{4}=75$$

$$\therefore$$ Sum invested at 5% per annum = $$100\times75=Rs.$$ $$7500$$

=> Ans - (C)