Adding a negative is the same as subtracting, so here we have 5/8-5/6. Let's find our least common denominator to use as our common denominator for both fractions. That would be 24. So, we multiply 5/8 by 3/3 because to get an equivalent fraction, you multiply by a version of 1- then you multiply 5/6 by 4/4. So, you get 15/24-20/24 equals -5/24. Hope this helps!