When fractions are written in their simplest form then it is known as the simplest form of fraction. The number which you have given above does not give clear meaning therefore, I am solving it with two ways.

If it is 16/20 the simplest form is as follows:

16/20 = 2 x 2 x 2 x 2/2 x 2 x 5

16/20 = 4/5

If it is 16.20 then simplest form is as follows:

16.20 = 1620/100

1620/100 = 5 x 2 x 2 x 81 /5 x 2 x 2 x 5

1620/100 = 81/5

If it is 16/20 the simplest form is as follows:

16/20 = 2 x 2 x 2 x 2/2 x 2 x 5

16/20 = 4/5

If it is 16.20 then simplest form is as follows:

16.20 = 1620/100

1620/100 = 5 x 2 x 2 x 81 /5 x 2 x 2 x 5

1620/100 = 81/5