Vintage (circa 1975) dress suit

I purchased this suit for Easter about 1975. As I remember it, I paid about $125 for it, which was a lot of money for me back then. The tag has 20B on it. Not sure what that means. I hace seen items with this tag listed as Large. I think it would be an 18 now. It is knit. The tag says handwash or dry clean. I wore it to church, almost exclusively. It is in excellent condition.