So what you need to do is make the denominator the same for all the fractions.
1/6 1/8 1/8 1/3
6, 3, and 8 all go evenly into 24 so...
you would change 1/6 to 4/24
you would change both 1/8 to 3/24
lastly you would change 1/3 to 8/24
Now the last step is to add all the fractions...
4/24+3/24+3/24+8/24=18/24