To add mixed numbers like you have here, you first have to convert them into fractions.
To do this, multiply the whole number part of the mixed number by the denominator, and add that value to the numerator.
So, 5 5/8 would become 45/8, because 5 x 8 = 40, and 40 + 5 = 45.
Likewise, 11 5/8 would become 93/8, because 11 x 8 = 88, and 88 + 5 = 93.
This gives us 45/8 + 93/8.
Now, to add the fractions. The two fractions have the same denominator already, so it is easy to add them. Simply add the numerators and keep the denominator the same.
The result of this is 143/8.
To simplify this to mixed number form, divide the numerator by the denominator. This results in 17.875. This means that 17 is your whole number part of the mixed number.
To find out how many eighths you'll have, multiply the 17 you just got by the denominator (8), and subtract the result from your large numerator. 17 x 8 = 136, and 143 - 136 = 7.
Your final result is 17 and 7/8.
