The equation for a line can be represented by the formula y=mx+b. M is the slope or rate of change and b is the y intercept. Since the equation y=5/2 does not have an x in it the slope is 0 and you have a perfectly straight horizontal line. Since we are just left with 5/2 that is our y intercept.
In other words, no matter what value you plug in for x, y will always be 5/2.
