Convert from firkin [butter, soap] to hundredweight [long, UK]

Unit Definition (firkin [butter, soap])
The firkin [butter, soap] is a traditional unit of weight for butter and soap, equal to 4 stone or 56 pounds (about 25.40 kilograms).

Unit Definition (hundredweight [long, UK])
The hundredweight is a traditional unit of weight equal to 1/20 ton. The hundredweight is the English version of a commercial unit used throughout Europe and known in other countries as the quintal or the zentner. In general, this unit is larger than 100 pounds avoirdupois, so to fit the European market the hundredweight was defined in England as 112 pounds avoirdupois (about 50.8023 kilograms) rather than 100 pounds. This definition apparently dates from about the middle of the 1300's. The British hundredweight was divided into 4 quarters of 28 pounds, 8 stone of 14 pounds, or 16 cloves of 7 pounds each. To distinguish the two hundredweight units, the British version is often called the long hundredweight and the American is called the short hundredweight or cental.