Answer:
y= -1x+(-3) or y= -1x-3 (because a positive and negative sign together equal a negative)
Explanation:
The slope-intercept form is y=mx+b. In the equation for slope-intercept form m=slope and b=y-intercept. You have the slope and y-intercept so all you have to do is put them in the right places. Since the slope is -1 your put the -1 where the m is and get y=-1x+b. Then since you know the y-intercept is (0,-3)= -3 then you just need to put the -3 where the b is to get y= -1x+(-3).