To find the value of \( y \) when \( x = -10 \) in the second equation, we can substitute \( -10 \) for \( x \) in that equation. The second equation is:
\[ y = x - 7 \]
Now, substituting \( -10 \) for \( x \):
\[ y = -10 - 7 \]
Calculating that gives:
\[ y = -17 \]
Thus, when \( x = -10 \) in the second equation, the value of \( y \) is:
\[ \boxed{-17} \]