As this line is perpendicular to the line y=-4/3x+5 , so it has une equation: y=3/4x+b, b is unknown. ( you know that a*a'=-1)
IN addition, this line pass through the point (5;-4) and we have x=5 and y=-4
so, -4=3/4 x 5 +b and b=-4-15/4=-31/4
And we have y=3/4x-31/4
Have fun