To use the additive inverse to find \( 23.45 - 68.7 \), we can rewrite the subtraction as the addition of a negative number:
\[ 23.45 - 68.7 = 23.45 + (-68.7) \]
Now, we can perform the addition. First, let's compute \( 23.45 + (-68.7) \):
- Convert \( 68.7 \) to its negative additive inverse: \( -68.7 \).
- Line up the numbers for addition:
\[ \begin{array}{r} 23.45 \
- (-68.70) \ \hline \end{array} \]
- Add the values:
\[ 23.45 - 68.70 = 23.45 + (-68.70) = -45.25 \]
Thus, \( 23.45 - 68.7 = -45.25 \).
Therefore, the correct response is:
\(-45.25\).