You have to set up a system of equations
x+y=104
3x-y=104
Sodas = 78
Hotdogs = 26
subtract the 26 1/2 from 76 and then divide by 2
76-26 1/2 = 49 1/2 / 2 = 24 3/4
In the given graph, lets mark two points:
Let
and 
The slope of the line is given by:



The equation of the line is given by:






Therefore, the function equation represented by the graph is: 
Answer:
A?? because I think it's not linear because it's not proportional