The slope-intercept form of the equation of a line is
y = mx + b
where m = slope, and b = y-intercept.
Now compare the form above with what you are given.
y = mx + b
y = 1/2x
You can write your equation as y = 1/2x + 0.
That shows that the slope, m, is 1/2 and the y-intercept, b, is 0.
