4x + (-3) = 8
(Hopefully)
As for the second one, I ASSUMED it would be this but I'm kinda busy and my ADHD brain just needed a break from what I was doing so just equate it for me, will you? And tell me if I was right or wrong because I have NO IDEA what I'm doing.
Let the number of days he trains for be x
So, 115x = 690