Cara nomor 18 dan 19 apa ya?

18
m = y/x
m = 8/12 = 2/3

19
mg = y/x = 4/-4 = -1

mg x mh = -1
mh = 1

y-y1=m(x-x1)
y - 0 = 1 (x - (-4))
y = x + 4
0 = x + 4 <== Garis berpotongan pada titik X maka, (y = 0)
x = -4

x = c