To subtract these mixed numbers and fractions, we first need to convert all the mixed numbers to improper fractions.

6-13 1/4 = 6 - 53/4 = 24/4 - 53/4 = (24 - 53)/4 = -29/4

1 - 0.8 = 1 - 8/10 = 10/10 - 8/10 = 2/10 = 1.2

-9 4/5 = -9 - 4/5 = -45/5 - 4/5 = (-45 - 4)/5 = -49/5

So, the expression becomes:

-29/4 - 1.2 - 49/5

Now, let's find a common denominator for all three fractions, which is 20:

-145/20 - 12/10 - 196/20

Now, add the fractions:

-145/20 - 24/20 - 196/20 = -365/20

Therefore, the final answer is -365/20 or -18 1/4.