The answer is not really simple. Well, it could be but there are a lot of things to look at here. You did not mention if the cable has Aluminum or Copper conductors. Could make a difference here. You didn't say how many "several years ago" was. The conductors could be 60ｰ, 75ｰ or 90ｰ rated. Are they type UF, THWN, THHN, THWN-2, XHHW, XHHW-2? It makes a difference.
Let's say it's copper type THWN-2 and they were 90ｰ rated, such as in type NM-B cable.
First, NEC Article 110-14 says if the circuit is under 100A then the conductors need to be used at their 60ｰ rating, unless all terminations in the circuit carry a higher rating. #6 copper at 60ｰ is able to be used at no more than 55A. However, there is a way out here. According to NEC 240.6, 55A is not a standard fuse/breaker size so you are allowed to round up the the next standard size which is 60A. So if you had a 6-3 type NM-B cable run, you are good to go with a 60A breaker on a 45A load.
Now, let's say it is Aluminum conductors.
#6 at 60ｰ is only good for 40A according to NEC 310.16 and 110.14
So I need more info to accurately answer your question. Post what cable type was run and I'll try to help more.
