4/5 Is the answer.
Here's why
4/5 and 0.75
4/5 is really 0.8 which can be written as 0.80 without altering its value.
Now compare 0.80 and 0.75, 0,80 is greater than 0.75 so 4/5 is greater than 0.75
Another method:
4/5 and 0.75
0.75 is really 3/4
Compare 4/5 and 3/4 or 16/20 and 15/20, obviously 16/20 is greater than 15/20 so 4/5 is greater than 0.75