Need step by step instructions

I am guessing 10/24th's- 9/24th's.
It is the smallest number both will divide into.

Like Stratmando said, find the least common denominator. 5/12 = ?/LCD and 3/8 = ?/LCD. Subtract and solve.

You could write down a list of multiples.
12
24
36
48, further if you need then, starting at the 12 see if 8 goes into it, and so on, until it can.
The most it could be, would be 12X8.