Let the sum invested be a
If a had been invested at 3% more interest then it would have earned $72.00 more for 2years.
So, the 3% of the amount a invested for 2 yrs = $72.00, so interest for 1yr = $36.00
a * 3% = $36.00
so, a = $36.00/3%
a = $1200.00
Thus, the money put on interest is $1200.00