Which equation represents the relation that is shown in the graph?

Cost of Buying Comic Books
On a coordinate plane, a graph titled Cost of Buying Comic Books has number of issues on the x-axis and total cost on the y-axis. A line goes through points (0, 0), (1, 3.5), (2, 7).

y = x + 2/7
y = x + 7/2
y = 2/7 x
y = 7/2x