There are many ways to do this, but the systematic way to to get common demoninators everywhere. In this case, that means converting the mixed fractions into simple fractions - each with demoninator 8. Then combine them (subtract them). Then, if necessary, write the result as a reduced mixed number (do the division and write the remainder in fraction form).
I'll do one step to get you started:
Now do the same thing for , and then you'll be ready to subtract them.