first u would take the 18 and - it on both sides
18 - 18 - 4x = -2 - 18 
which would be 
-4x = -20 
then u would divide 4 on bothe sides 
-4x/4 = -20/4
which would give u 
- x = - 5
this is the answer for the negative x 
for positive u would flip the answer 
so 
x = 5 which then = 4
x=5 is ur answer 
hope this helps or u understand wat im sayin