The problem looks like 1/(4/5)
Well just like when you are dividing two fractions...
(a/b)/(c/d)=(a/b)*(d/c)=(ad/bc)
In this case:
(1/1)/(4/5)
(1/1)*(5/4)=5/4 which is an improper fraction so:
(4+1)/4=1+1/4
1 1/4
Now the title of your question was 3/4/5 so
(3/4)/5=3/20
