#### Answer

675 dollars are invested at 3%.
1425 dollars are invested at 5%.

#### Work Step by Step

Let X represent the amount invested at 3%.
Thus, the remainder, which is 2100 - X, is invested at 5%.
The interest earned by the 3% investment is equal to 3% $\times$ X = 0.03X.
The interest earned by the 5% investment is equal to 5% $\times$ (2100 - X) = 105 - 0.05X.
Since the interest earned by the 5% investment is 51 dollars more than the interest from the 3% investment, we set up the following equation:
105 - 0.05X = 51 + 0.03X
105 = 51 + 0.08X
54 = 0.08X
Divide both sides by 0.08.
X = 675
675 dollars are invested at 3%.
2100 - 675 = 1425 are invested at 5%.