Keep the denominators the same and subtract the numerators. So for example in your example:
7/8 - 3/8
Leave the 8 alone. Subtract 3 from 7.
7 - 3 = 4
So answer is:
4/8
Sometimes they may have to simplify the answer, and in this case, 4/8 could be simplified to 1/2
Given the following question:

Graph the function:
The value of the function of x is infinite as you see the line goes on forever. Which means your answer is option C or "10,000."
Answer:
-348.33
Step-by-step explanation:
Use PEMDAS as your guide.
(-342-8) - (-5/2+1)
PEMDAS
parenthesis
-350 - (-5/3)
PEMDAS
Dvisision
-350- (-1.67)
= - 348.33
Hope this is what your looking for!