X+y=7
2x-y=2

how do i graph this?

First you will need to solve the equation for x 
x = 7 - y
2x - y = 2
next you will substitute the given value of x into the equation 2x - y = 2
2(7 - y) - y = 2
now you will need to solve the equation for y
y = 4
then you will need to substitute the given value of y into the equation x = 7 - y
x = 7 - 4
now you need to solve the equation for x 
x = 3
the possible solution of the system is the ordered pair (x,y)
(x,y) = (3,4)
check if the given ordered pair is the solution of the system of equations
3 + 4 = 7
2 x 3 - 4 = 2
now simplify the equalities 
7 = 7
2 = 2
since we know all of the equalities are true, the ordered pair is the solution of the system
(x,y) = (3,4)
this means that the first line will go through 7 on the y axis, and the second line will go through 1 on the x axis. the two lines will intersect at the point (3,4) making it look like an X.
let me know if you have any further questions about the question.
:)

No solution : there is no number of boxes that she bought