To find x, set the equation equal to zero
4x-20=0
the next step is to isolate the variable, you can do this by adding 20 to both sides, remember when you change one side of the equal sign you must do the same to both
4x=20
now you can divide by 4 to get x by itself, again divide both sides of the equation
4x/4=20/4
x=5
After doing the division we see that x is equal to 5, and you can always check to see if your answer is correct by plugging it back into the equation:
4(5)-20=0
20-20=0
Hope this helps :)