y = (-1/2)x - 6
y = (-1/2)x + (-6)
Suppose you are given a line of the form y = mx + c, where m and c are some real numbers. Then m will be the slope and c will be the y-intercept.
Notice from y = (-1/2)x + (-6) that m = -1/2 and c = -6
This means the slope is -1/2 and the y-intercept is -6