You can do it like this to get the middle number.
MID gives you a string starting at a given character, and of specified length.
We find the first ";" by using FIND and use it for the start.
Now we need the length, and for that we have to find the second ";" as well, and we do it again by FIND, but starting at the position after the first ";". This part gives us position of the 2nd ";":
From that, we substract the position of the 1st ";" to get the length and combine everything in the formula above. Note that if your cell doesn't have at least 2 semicolons, the formula will return an error.
If you need the last number, you need the 2nd ";", so you could use:
To get the first number is the simplest: