You could convert them into improper fractions first. 7 7/8 should become 63/8 and 3 1/4 should become 13/4. Then, change both fractions so they share a common denominator. I'll use 8. 63/8-26/8 = 37/8, which is then converted into 4 5/8. Hope that helped you.
First we find the common denominator for the fractions. The first number that both 8 and 4 will go into is 8, so we will use 8.
We do not need to change the first number, as it is already in eighths.
For the second fraction: We can change 4 to 8 by multiplying by 2. Whatever we do to the denominator, we must do to the numerator, so we have 1*2 = 2. This gives us
