Solve Decimal Addition: 15.6 + 7.8 Step by Step

To solve this problem, we'll add two decimal numbers $15.6$ and $7.8$.

• Step 1: Align the decimal points of the numbers, writing them one under the other:

  $\begin{array}{c} 15.6 \\ + \ 7.8 \\ \hline \end{array}$

• Step 2: Add the numbers starting from the rightmost digit, which are the tenths after the decimal point:

  $6 + 8 = 14$. Place $4$ under the tenths column and carry over $1$ to the next column (the units column).

• Step 3: Add the numbers in the units column, considering the carry:

  $5 + 7 = 12$; with the carry $1$, it becomes $12 + 1 = 13$. Place $3$ under the units column and carry over $1$ to the next column (the tens column).

• Step 4: Add the numbers in the tens column, considering the carry:

  $1 + 0 + 1 = 2$ (as $15.6$ can be seen as $015.6$, for alignment purpose). Place $2$ under the tens column.

• Step 5: After adding all decimal digits, position the decimal point in the result directly below where the other decimal points are aligned in the original numbers.

Thus, the sum of $15.6 + 7.8$ is $23.4$.

Finally, checking against the answer choices, we find that $\boxed{23.4}$ matches the correct answer choice.