When we divide a fraction by a number, that's equivalent to multiplying the first fraction by the inverse of that number.
In this problem, we need to divide the fraction 5/4 by 20. So we obtain:

Now, we need to multiply the numerator of the first fraction by the numerator of the second one, and the denominator of the first fraction by the denominators of the second one:

Now, we need to simplify the answer. To do so, we can divide both the numerator and the denominator by 5:

Therefore:
Each piece is 1/16 m long.