To solve the expression \( 8.7 - (-4.6) \), we need to remember that subtracting a negative number is the same as adding the positive number.
So, we can rewrite the expression as:
\[ 8.7 + 4.6 \]
Now, let's calculate:
\[ 8.7 + 4.6 = 13.3 \]
Thus, the answer is \( 13.3 \).