Answer:
(12, -3)
Step-by-step explanation:
You can solve it algebraically or graphically. Graphically you find the intersection point. Algebraically with substitution/elimination.
Answer: 128 pieces of candy for all the cookies.
For A B and C, you just plug in the given number
A

B

C

And for D, you set the equation to 26 and solve for n

I had to use x instead of n, but for D n=7. :)