This is a problem in fractions, so merely dividing to get a decimal answer isn't the correct solution.
You need to change each fraction to one with a common denominator. The smallest common denominator for 1/4 and 1/6 is 12. You must multiply the denominators by some value that will result in the number 12. Mulitply 5/6 by 2/2 (same as mulitplying by 1, so the value doesn't change); multiply 3/4 by 3/3 (same explanation).
(5/6) * (2/2) = 10/12 (multiply the numerators to get 10; multiply the denominators to get 12)
(3/4) * (3/3) = 9/12 (multiply the numerators to get 9; multiply the denominators to get 12)
Now, it is obvious that 5/6 is larger than 3/4