To solve this, we first need to simplify the expression within the parentheses:

6 11/15 = 6 + 11/15 = 90/15 + 11/15 = 101/15

Now we can substitute this back into the original expression:

20 - 18,6:(101/15 - 4,15)

Next, we convert the division to multiplication by flipping the fraction:

20 - 18.6 * (101/15 - 4.15)

Simplify inside the parentheses:

20 - 18.6 * (96.85/15)

Now perform the multiplication:

20 - 1188/15 = 20 - 79.2 = 119.2

So the final answer is 119.2