enum class BookType (val myValue: Int)
{
     Unknown (10),
     Fantasy (15),
     History (27),
     Child (28),
}

fun main() {

     // find by Int value
     val myEnum:BookType? = BookType.entries.firstOrNull(){ it.myValue == 15 }
 
     // 2-ой способ:
     // val myEnum:BookType? = BookType.values().firstOrNull(){ it.myValue == 15 }

     if (myEnum!=null)
     {
          println(myEnum.myValue)
          println(myEnum.name)
     }
}