Solve Decimal Addition: 10.03 + 5.51

To solve this problem, we'll follow these steps:

• Step 1: Align the numbers by their decimal points.

• Step 2: Add the numbers starting from the rightmost digit, moving left.

• Step 3: Handle any carryovers properly.

Now, let's work through each step:

Step 1: Align the numbers:

  10.03
+    5.51

Step 2: Start adding from the rightmost digit (hundredths):
$\begin{array}{c} & 10.03\\ + & \,5.51\\ \hline & 15.54\\ \end{array}$

Step 3: Add the digits from right to left:
- Hundredths place: $3 + 1 = 4$
- Tenths place: $0 + 5 = 5$
- Whole numbers: $0 + 5 = 5$, $1 + 0 = 1$

Thus, the sum of $10.03$ and $5.51$ is $\textbf{15.54}$.

After evaluating the answer choices, the correct answer is choice 3: $\textbf{15.54}$.