`23.143 + 17.159 = "_____"`.

Options

A. `40.202`
B. `40.322`
C. `40.302`
D. `40.312`

Explanation

To solve the problem \( 23.143 + 17.159 \), we will add the two decimal numbers step by step.

### Step 1: Align the Numbers
First, we need to write the numbers one below the other, aligning the decimal points.

```
23.143
+ 17.159
```

### Step 2: Add the Thousandths Place
Start from the rightmost column (thousandths place):
- \( 3 + 9 = 12 \)
- Write down \( 2 \) and carry over \( 1 \).

### Step 3: Add the Hundredths Place
Next, move to the hundredths place:
- \( 4 + 5 = 9 \)
- Add the carry over \( 1 \): \( 9 + 1 = 10 \)
- Write down \( 0 \) and carry over \( 1 \).

### Step 4: Add the Tenths Place
Now, move to the tenths place:
- \( 1 + 1 = 2 \)
- Add the carry over \( 1 \): \( 2 + 1 = 3 \)
- Write down \( 3 \).

### Step 5: Add the Units Place
Next, move to the units place:
- \( 3 + 7 = 10 \)
- Write down \( 0 \) and carry over \( 1 \).

### Step 6: Add the Tens Place
Finally, add the tens place:
- \( 2 + 1 = 3 \)
- Add the carry over \( 1 \): \( 3 + 1 = 4 \)
- Write down \( 4 \).

### Final Result
Putting it all together, we have:

```
23.143
+ 17.159
---------
40.302
```

Thus, the sum \( 23.143 + 17.159 = 40.302 \).