Convert from quartern-loaf to arroba [Spain]

Unit Definition (quartern-loaf)
The quartern-loaf is a traditional English unit of weight for bread. A quartern-loaf is made from a quartern of flour. The finished loaf usually weighs somewhere between 4 and 5 pounds (very roughly 2 kilograms).

Unit Definition (arroba [Spain])
The arroba [Spain] is a traditional unit of weight in Spain and Portugal, equal to 1/4 quintal. However, the Spanish and Portuguese quintals are of different sizes. In Spain, the arroba equals 25.36 pounds (11.50 kilograms); arrobas of very similar sizes were established in the Spanish speaking countries of Latin America. The arroba has also been used as a metric unit equal to exactly 15 kilograms. The name of the unit comes from ar rub', Arabic for "the quarter."