First convert 0.75 into a fraction: 75/100=3/4. Now we have three fractions 7/12, 3/4, 5/6. The easiest way to compare them is to use a common denominator, which in this case is 12.
7/12 is already in twelfths, 3/4=9/12 and 5/6=10/12 because 3/4 of 12 is 9 and 5/6 of 12 is 10. Now all we do is compare numerators: 7, 9, 10. They're already in order least to greatest.