Question 21038
Let "x" be the amount invested at 3%
Then "3x" is the amount invested at 5%
Equation:
 0.03x + 0.05(3x) = 3600
    3x + 15x = 360000
         18x = 360000
   x = $20,000  (amount invested at 3%)
  3x = $60,000  (amount invested at 5%)

Cheers,
Stan H.