To calculate \( 45.678 - 23.1 \):
\[ 45.678 - 23.1 = 22.578 \]
Now, we must determine the number of significant digits in the answer. The numbers involved have the following significant figures:
- \( 45.678 \) has 5 significant figures.
- \( 23.1 \) has 3 significant figures.
When performing subtraction, the result should be rounded to the least number of decimal places of any number in the operation. The number \( 23.1 \) has 1 decimal place, while \( 45.678 \) has 3 decimal places. Therefore, the result should be rounded to 1 decimal place.
Rounding \( 22.578 \) to 1 decimal place gives us \( 22.6 \).
The final answer is \( 22.6 \), which has 3 significant figures.