There is only one solution since they have different slopes.
x + 2y = 5 /* (-1)
3x + 2y = 9
__________
-x - 2y = -5
3x + 2y = 9
add these two equations
_______________
2x = 4
x = 4/2 = 2$ for a hotdog
2y = 5 - x = 5 - 2 = 3 => y = 3/2 = 1.5$ for a hamburger
Where are the equations and then I am happy to help.

=0 is the answer
Factor it (x+3)(x-1)
Set each to 0 x+3=0 and x-1=0
Solve each for x x=-3 and x=1
Ta da :)
Hope that helps
B because you already know number of cookies eaten, you dont know if the total was 12 cookies because you dont know how many days so, if you dont know how many days then y would be the number of days... Good Luck