To solve these expressions, we will perform the following calculations:

3/4 : 5/8
Convert 3/4 to 6/8 to make both fractions have the same denominator.
(6/8) : (5/8) = 6/5 = 1 1/5

3 1/9 : 2 4/15
Convert mixed numbers to improper fractions.
(28/9) : (34/15) = (28/9)/(34/15) = (28/9)*(15/34) = 5/3 = 1 2/3

0.8 : 4 4/5
Convert 0.8 to a fraction by dividing 8 by 10.
(8/10) : (24/5) = (8/10)/(24/5) = (8/10)*(5/24) = 1/6

2 2/19 (2 3/8 : 1 1/4)
Convert mixed numbers to improper fractions.
(40/19) (19/8) = 40/8 = 5

So, the answers are: