When dividing by zero you can’t divide anything With it and it can’t equals zero because that would be wrong it would have to be undefined
let
x-------> walnuts that Mario eats in a week
y-------> walnuts that Yolanda eats in a week
we know that
x=2y-------> equation 1
y=6*7-------> y=42 walnuts
substitute the value of y in equation 1
so
x=2*42-----> x=84 walnuts
therefore
the answer is
Mario eat in a week 84 walnuts
1) -15
2) 5
3) -13
4) -4
5) 5
6) 14
7) 0
8) -8
9) -8
10) 7
These are very easy, when subtracting a negative from a positive think of it as just plain subtraction. When adding a negative to a positive, again, think of it as subtraction. When subtracting two negatives it's basically addition but you final answer should have a negative sign.
Hope I could help! :)
Is there a picture or something that shows other things he's done to help answer the question?