I'll play devil's advocate here. Tbh, I think that if Hyesung knew his mom was left alone to fend for herself he'd probably feel very guilty for not keeping in touch. Dojin should've talked to him before stepping to help out, but I see it as a "if Hyesung ever found out, at least he doesn't have the guilt of his mother suffering on his conscious" move
Where did that 2 come from???
Yeah, i think it was just a translation mistake on the chalk board, because she specifically called it linear equation in her thought bubble, and her work process was definitely linear equation. But the wrong translation made it look like the initial question was just a basic addition/subtraction word problem.










Let's just throw the whole garbage excuse for a father away.