We can solve this using inverse operations & “working backwards.”
Addition is the inverse to subtraction, so we’ll subtract 20 from 830.
830 - 20 = 810
From there, since division is the inverse to multiplication, we’ll divide 810 by .9 .
810/.9 = 900
Therefore, x is equal to 900.
You can check this answer by working through it forwards. (900 x .9 = 810, 810 + 20 = 830.)
Hope this helped! :)