find the slope of a perpendicular to each given line y=-x-3 and y=x-4
two lines are perpendicular if their slopes are negative reciprocals. That is, their product is -1.
y = -x-3
has slope -1. So, its reciprocal has slope -1/-1 = 1
y = -x-3
has slope -1. So, its reciprocal has slope -1/-1 = 1