To find \( f(-1) \) using the function rule \( f(x) = -3 - \frac{10}{x} \), we can substitute \( -1 \) for \( x \).
So,
\[ f(-1) = -3 - \frac{10}{-1} \]
Calculating the fraction:
\[ f(-1) = -3 - (-10) \]
This simplifies to:
\[ f(-1) = -3 + 10 \]
Therefore:
\[ f(-1) = 7 \]
So, the final answer is:
\[ f(-1) = 7 \]