Answer:
Option C
The student's conclusion is correct because the solution to the system of equations
and
is 
Step-by-step explanation:
Let
x------> the cost of each burger
y-----> the cost of each sandwich
we know that
-----> equation A
----> equation B
Solve the system of equations
Multiply the equation B by 
----->
------> equation C
Adds equation A and equation C

Substitute the value of x in the equation B



The solution of the system of equations is the point 
so
The price of each burger is 
The price of each sandwich is 