Many of the answers given are listing 26 characters as your character set, but that's not correct. It would have to be at least 52 for both capital and lowercase characters. If you were brute forcing though, you couldn't know if it was just letters without numbers or punctuation. So the standard number of characters is 94, 26 A-Z, 26 a-z, 10 for 0-9, and 32 "special characters" for punctuation.
Now, to fully brute force this, you have to know the "password" length (let's just call MynameisJames a password) so 13 characters. You typically do not know this information, so what happens is you start by brute forcing everything for 4 characters, then everything for 5, and keep increasing until you find it.
This can be very tedious. Even with a cracking rig that had an i7 and 2 1080 graphics cards, brute forcing a 10 character MD5 hashed password could take a week, and that is assuming I knew it was 10 characters. Granted, there is more involved with that because it's actually cracking the "hash", so the computer has to generate a hash for each tested entry and that takes longer.
"How difficult would it be" is a difficult question to answer as it's not particularly measurable. That said, a week with a crypto computer would probably guess this correctly if it was in an outdated hash format (MD5). In the sense that this is just raw plain text, it would probably more like trying to enter a password, as opposed to cracking a hash, which takes much longer because you have to wait for a response from that. If it was a script to just guess an unknown plaintext 13 character that was entered, could take a few days if optimized (I wrote a script like this to test the success of password lists, so I can say first hand it would run 4 million attempts in a few hours).
13 character password with a 94 character set brute force is 44 x 10^24 attempts. The divided by 2 method just gives you a 50% chance and my experience is the password always seems to be in the 2nd half of that 50, just murphy's law of "in practice" vs "in theory".
This article might also be helpful https://www.password-depot.com/know-how/brute-force-attacks.htm