Tarun invested Rs 'a' at 11% per annum simple interest for 4 years and Rs. 'b'  at 10% per annum compound interest for 2 years. Shalu invested Rs 'b + 1000' at 12.5% per annum simple interest for 1 years and Rs. 'a + 1000'  at 20% per annum compound interest for 2 years. If the total interest earned by Tarun and Shalu is Rs 1510 and Rs 1820 respectively. Find the interest earned by Neha if she has invested Rs. 'a + b' for 3 years at a simple interest rate of 12%.