The traditional dragon is a reptile, but on my planet (Zavnious) there are warm-blooded dragon-like creatures that are covered in fur. They have a thick skin instead of scales and they do not breath fire. They live in the caves found in sandstone cliffs in groups of up to twenty individuals — two of which may be adolescents, if a female is pregnant they will remain in the cave, the other members of the pack will return with a potion of the kill. This will continue until the infant is born. When their pack exceeds twenty the alpha will no longer accept new members, displacing by force if necessary.
They fly at high speeds of roughly 100km/h, can grow to lengths of 15m and weigh 2780-2.5 tonnes970Kgs (ifhopefully this is unrealistic please suggest an alternativemore realistic). They are carnivorous and hunt in packs praying on the large (about three times the size of a cow), slow moving herbivores that roam the western shrub plains. They mostly rely on their eyesight for hunting, which is very good.
Now this is my question: What wingspan would they require?
If I have left out any major aspects of their biology please highlight it in the comments.
Zavnious is desert planet with 1.26G and an earth-like atmosphere.