Convert the mixed number to an improper fraction.

6 7/8

55/8
Improper fraction: A fraction in which the numerator is greater than the denominator
What you will do: Multiply your whole number by your denominator, which means multiplying 6 by 8. 
You will get: 48
Next: You will take your 48 and add your numerator to it. You will be adding your 48 to your 7
You will get: 55
Then: You will take your 55 and you will put it over your denominator, which is 8 and your done.
REMEMBER: When trying to turn a mix number into a improper fraction you will always keep your denominator the same.

HOPE THIS HELPS! ^_^