Convert from livre [France] to arroba [Spain]

Unit Definition (livre [France])
The livre is a traditional unit of weight in French speaking countries and in Greece. The livre corresponds to the English pound and to the Spanish libra. The livre is divided into 2 marcs or into 16 onces. The French livre varied from market to market, but the official standard from about 1350 to the introduction of the metric system was the livre poids de marc or livre de Paris of 489.5 grams (1.079 English pounds). In modern France, the livre is used as an informal metric unit equal to exactly 500 grams or 0.5 kilogram (1.1023 pounds). The traditional Greek livre is also about 500 grams.

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."