Respuesta :
-7(2+1)
-7(3)
-21
negative X positive = negative
positive X positive = positive
negative X negative = positive
These simple rules might help with your question.
Hope this helps!
Step-by-step explanation:
We have a rule that says : Â -ab = -(ab)
Then  -7 (3) = -(7×3) = - 21
by the way :
 (-7) + (-7) + (-7) =(-7)×3 = -7(3)
:)