Armor gains more strength for the amount of xp

Hi, I'm trying to make armor and tools, which increase their strength respectively with the player's XP value, if he has 80 xp the sword will have 80 damage, if he has 90 XP the armor will have 90 protection.

 
My procedure doesn't work, and I tried writing the code manually but it also looks like it's incompatible or some error that I can't find or understand for now, the procedure doesn't work as expected, I tried to get some ready from the internet but nothing that is useful, if you can help me I would appreciate it