To solve the equation \( x + 11 = -17 \) for \( x \), you should isolate \( x \) by eliminating the \( +11 \) on the left side.
To do this, you should subtract 11 from both sides of the equation.
So, the correct operation to perform on both sides of the equation is:
Subtract 11.
This will give you:
\[ x + 11 - 11 = -17 - 11 \]
Simplifying that will yield:
\[ x = -28 \]