7. A pony and a donkey together carry 120 catties of rice. The owner first takes some rice from the pony and puts it on the donkey, making the donkey carry twice as much. Then, he takes some rice from the donkey and puts it on the pony, making the pony carry twice as much. At this point, the pony and the donkey carry the same amount of rice. The pony initially carried catties of rice. $\qquad$
75