Your question is ambiguous, since it can be read as either (6+6)/4 or as 6 + 6/4, which are two different amounts. The former is 12/4 = 3, and the latter is seven and a half.
4/6 = 2/3
6/24 in simplest form is 1/4 (1 over 4)
4 over 24 is 1 over 6 in its simplest form.
3/25/6 + 4/6 = 9/6 or 3/2 in simplest form
6/8 is 3/4 in simplest form.
24/6 = 4/1 => 4 in its simplest form
27/4
2/3
1/4
1/6
two thirds
1/6