The Distributive law is used here. Can you expand the brackets?
The idea of these problems is to get all of the unknown(in this case x) on one side and the numbers on the other.
Firstly , expand all the brackets.
This can be done by multiplying 2(the factor) into the bracket.
(nothing changes on the right side)
Now, 'move' the x to the left side and the 8 to the right side.
Subtract 8 and 4x from both sides.
Solve the other problems in the similar fashion. Hope this helps.