Answer:
1) c. 10
2) a. 1 and 18
3) d. 17
4) I think it's actually 12 but I don't know
For Q3, you can subsitute x = 2 and y = 5 into the systems
-5(2) + 5 = -5
so it's a solution for the first system
-4(2)+2(5) = 2
it's also a solution for the second system
You would have to add a positive 6 to the negative 6 to get zero. Lets say you have -2 in order to get it to zero or just any positive number, you have to add a positive of the same value or higher to be able to get it there. I hope you understand that.