We want to isolate x. One nice way of doing this is to multiply both sides of this equation by 9, as 9/9 is just 1 (one). We then get:
9(9/81) = x, or 81/81, or 1. x = 1.
Note that you could obtain the same result by reducing the fraction 9/81 to 1/9 and then noting that 1/9 = x/9. It's obvious that x = 1 here.
