The best way to solve this is to find a common denominator! Don't worry, it's super easy
Take 4 1/5 and change it to a single fraction by multiplying 5(4) and adding the 1, then put it over 5 again. This gives you 21/5, which is equal to 4 1/5.
Then do the same thing with 2 1/2:
2(2) +1 over 2= 5/2.
The problem is asking you to subtract. So 21/5- 5/2.
So how can you subtract that? Easy: common denominators!
The smallest number that is divisible by both 2 and 5 is 10, so you want both numbers to have 10 on the bottom.
To do this, multiply 21/5 by 2/2 (Note: 2/2 is equal to 1, so you are not changing the value of the fraction, you're only changing how it is written).
This is 42/10.
Then multiply 5/2 by 5/5 for 25/10.
NOW you can finally subtract!
42/10 - 25/10 = 17/10
17/10 is your answer!!
(Think 42-25/10 if you're confused on how to subtract Fractions)