Question 715579
How you plot and show the graph depends how you want your units.  

You might wish choosing increments of the denomination for increments of (1/2).  If that is your choice, then you would label your axes as 1/2, 2/2, 3/2, 4/2, 5/2, ... and on like that.  You could then show the line intersecting the y axis at 13/2.  


If you really wanted to show mixed numbers, integer plus fractions with increments of 1/2, then, naturally, you want to show the number on the y axis, including the y intercept, as {{{6&1/2}}}.


The way you display the numbers depends on how much of the graph you need to show.  The example you gave suggests that you want to label your axes in mixed number units with increments of 1/2 or 1/4.