Explanation:
A coefficent is a numerical or constant quantity placed before and multiplying the variable in an algebraic expression. Or in other words, the number being multiplied with the variable. For example, the 4 in 4x.
The expression is -x-10. If we go back to the definition, the coefficient combined to the variable is -1.
A variable like the 'x' in this expression can also be written as 1x.
So the answer is -1.
Hope it helps!