(1) Combining fractions is just a matter of writing each individual fraction in terms of a common denominator. The least common multiple of 6, 4, and 8 is
LCM(6, 4, 8) = 24
since 6×4 = 4×6 = 8×3 = 24. So
2/6 = (2×4)/(6×4) = 8/24
1 1/4 = 4/4 + 1/4 = 5/4 = (5×6)/(4×6) = 30/24
13 4/8 = 104/8 + 4/8 = 108/8 = (108×3)/(8×3) = 324/24
Then
2/6 + 1 1/4 + 13 4/8 = 8/24 + 30/24 + 324/24 = 362/24 = 181/12
(2) We have
LCM(12, 9) = 36
since 12×3 = 9×4 = 36. Then
121 2/12 = 1452/12 + 2/12 = 1454/12 = (1454×3)/(12×3) = 4362/36
781 6/9 = 7029/9 + 6/9 = 7035/9 = 2345/3