The slope of the red line is 4/1. Perpendicular lines always have opposite reciprocal slopes, meaning they have opposite signs (positive and negative), and flipped fractions (numerator is denominator). Hope this helps!
When two lines are perpendiculars, theirs slopes are opposite (sign) and inverse. If the green line has a slope of -1/4, the slope of the red line is +4/1=4
