Let's denote the unknown number as \( x \). According to the problem statement, we can set up the equation:
\[ 10(x + (-1)) = -40 \]
This simplifies to:
\[ 10(x - 1) = -40 \]
Now, we can divide both sides by 10:
\[ x - 1 = -4 \]
Next, we can solve for \( x \) by adding 1 to both sides:
\[ x = -4 + 1 \]
\[ x = -3 \]
So, the number is \(-3\).
The correct response is:
−3 (negative 3).