20 - 18,6 / (6 11/15 - 4 3/20)

First, convert the mixed fractions to improper fractions:

6 11/15 = (615 + 11) / 15 = 91/15
4 3/20 = (420 + 3) / 20 = 83/20

Now rewrite the expression:

20 - 18,6 / (91/15 - 83/20)

Next, find a common denominator to subtract the fractions:

The common denominator is 60, so:

91/15 = 364/60
83/20 = 249/60

Subtract the fractions:

364/60 - 249/60 = 115/60

Substitute back into the original expression:

20 - 18,6 / (115/60)

Now, divide 18,6 by 115/60:

(18*60 + 6) / 115 = 1104/115 = 9.626

Plug the result back into the expression:

20 - 9.626

Calculate the final answer:

20 - 9.626 = 10.374

Therefore, the final answer is 10.374.