Persamaan garis a adalah..

mb = - 3/4
karena tegak lurus maka
ma × mb = -1
ma = 4/3
(0,c)
(0,3)
y = mx + c
y = 4/3 x + 3

b (4,0) (0,3)
m = y2-y1 / x2-x1
= 3-0 / 0-4
=3/ -4
=-3/4

a tegak lurus b
maka

m1 x m2 = -1
-3/4 x m2 = -1
m2 = -1 x 4/-3
m2 = 4/3

garis a melewati titik (0,3)

y-y1 = m (x-x1)
y - 3 = 4/3 (x -0)
y-3 = 4/3x
3y-9 = 4x
3y-4x-9 = 0
atau
3y = 4x + 9
atau
4x-3y+9=0