A negative minus a positive is essentially a negative plus a negative! The two values will add on top of each other to create a larger negative number.
I'd recommend turning the mixed numbers into improper fractions: 25/8 and 5/2. Then, make sure their denominators are equal by multiplying 5/2 by a "big one" or 4/4. This should get you 20/8.
Now, solve for -25/8 - 20/8 to get -45/8. Turn that number into a mixed number, and you have your answer!
