Iget how to do a proportion in math ya know with cross multiply but what about if there is a variable subtracting the whole thing x- 1/5 = 3/5

X-(1/5)=(3/5)

x=(3/5)+(1/5)

x=4/5=0.8

The easiest way to solve this is to add  1/5  to each side of the equation.
When you do that, you immediately have  x = 4/5  and that's the solution.

(Note that you don't "move" numbers from one side to the other.  You add or
subtract the same number from each side.  And if it helps, you can also multiply
or divide each side of an equation by the same number.)

If you're comfortable with proportions, and you desperately want to turn this one into a proportion that you can cross-multiply, then you can turn the whole left side into a fraction over a common denominator.

        x - 1/5  =  (5x - 1) / 5

Now you have a proportion:

          (5x - 1)/5 = 3/5

and you can cross multiply it.