If I'm correct your equation is
3x+50=6x−10
Now we solve it
---------------
Subtract 6x from each side
3x+50−6x=6x−10−6x
−3x+50=−10
--------------------
Subtract 50 from each side
−3x+50−50=−10−50
-3x = -60
-----------------------
Divide each side by -3
-3x ÷ -3 = -60 ÷ -3
x = 20