Which equation could have been used to create this graph?

Y = mx, where m is slope.
Slope is , where:
  rise --> vertical(y axis)
  run --> horizontal(x axis)

y=4x: slope = 4

rise = 4
run = 1

So go up 4, and right 1

If you plot points starting at (0, 0) you get the graph shown to the right; or vice versa, counting the rise and run and finding the slope.

D