Who pays for what? - Carpet

[Cesar Gonzalez]

I recently inherited tenants and they put in a maintenance request for the carpet, the carpet separated between the seams in the living room and has a 2in gap between them (Possibly causing a tripping hazard), it also runs for about 10ft from one end of the room to the other. My question here is who pays for the carpet, I had someone come out and give me a quote for $400 to replace the carpet for the living room (Carpet is not repairable). Will this be considered EXESSIVE wear and tare? Can the tenant be liable for causing this? The tenants have been in the property for 3 years now. 

Any suggestions are always welcomed, thanks!