So what I did was I wrote down the problem 50 - 10x = 20.
The first step I did was take 50 and subtract it from both sides: 50 - 10x = 20
-50 -50
After that i cross out the so 50's and take 20 and subtract it to 50 which gave me -30. So when you write this down you rewrite it as: -10x = -30
Last step: take the -10 and divide it by both sides the cross out the two -10's cause it's going to be written as -30/-10 which would give you x = 3. So there is your answer, hope this helps. :)
~Shadow