Rashmita invests 20% of her Principal at 15% per annum for 4 years, 50% of the remaining at 20% per annum for 2 years and the rest at 12% per annum of 1 year at simple interest. If the interest is calculated on the whole sum, then find the rate of interest per annum.
1
22.8%
2
32.8%
3
33.8%
4
42.8%
5
None of these