The graph below shows a proportional relationship between [x] and [y]. What is the constant of proportionality,

[\dfrac{y}{x}] ? A graph on a Cartesian coordinate system with x and y-axes. The x-axis is marked with evenly spaced ticks in increments of 0.5, ranging from 0.5 to 4.5. The y-axis is marked with evenly spaced ticks in increments of 1, ranging from 1 to 9. The graph displays a single slant line starting from (0,0) with an arrowhead at its end. The line passes through a point marked with a filled dot at (1,3.5). The point (0,0) is marked with a filled dot as well. [\small{0.5}] [\small{1}] [\small{1.5}] [\small{2}] [\small{2.5}] [\small{3}] [\small{3.5}] [\small{4}] [\small{4.5}] [\small{1}] [\small{2}] [\small{3}] [\small{4}] [\small{5}] [\small{6}] [\small{7}] [\small{8}] [\small{9}] [y] [x]