Hi there!
There is four separate steps to solving for x here.
1) Simplify both sides.
To simplify, distribute first:
(5)(2x)+(5)(-4)=4+3x
10x+-20=4+3x
10x-20=3x+4
2) Subtract 3x from both sides.
10x-20-3x=3x+4-3x
7x-20=4
3) Add 20 to both sides.
7x-20+20=4+20
7x = 24
4) Divide both sides by 7.
7x/7 = 24/7
x = 24/7. Hehe, get it? :P
Hope this helps!