Answer :
To add the two numbers, we start with
$$
39.3 + 63.4.
$$
**Step 1.** Write both numbers with their decimal points aligned:
\[
\begin{array}{r}
\ \ 39.3 \\
+ \ 63.4 \\
\hline
\end{array}
\]
**Step 2.** Add the numbers column by column. The digits after the decimal point are added first, then the whole numbers.
- Adding the tenths: $0.3 + 0.4 = 0.7$.
- Adding the whole number parts: $39 + 63 = 102$.
**Step 3.** Combine the two sums:
$$
102 + 0.7 = 102.69999999999999.
$$
Thus, the final answer is
$$\boxed{102.69999999999999}.$$
$$
39.3 + 63.4.
$$
**Step 1.** Write both numbers with their decimal points aligned:
\[
\begin{array}{r}
\ \ 39.3 \\
+ \ 63.4 \\
\hline
\end{array}
\]
**Step 2.** Add the numbers column by column. The digits after the decimal point are added first, then the whole numbers.
- Adding the tenths: $0.3 + 0.4 = 0.7$.
- Adding the whole number parts: $39 + 63 = 102$.
**Step 3.** Combine the two sums:
$$
102 + 0.7 = 102.69999999999999.
$$
Thus, the final answer is
$$\boxed{102.69999999999999}.$$