O1 Audi A6 2.8 p0430 and p0420

Hi all. This is my first post to one of these. I just bought an 01 Audi A6 quattro 2.8 with 93000 miles on it. The CEL came on the other day so I got a reader and the codes read p0430 Catalyst Efficiency Below Threshhold (Bank 2)

and p0420 Catalyst Efficiency Below Threshhold (Bank 1). What could this meen and whats the solution if anyone knows thank you.