Ferb raises some cows and chickens. As a regular routine, he does a daily inventory of his animals. One day, he was so groggy that all he remembers is that he was able to count 75 heads and 264 feet, but he doesn't know exactly how many of each type of animal he has. How many cows does he have?
NOTE: All the cows have 4 legs and all chicken have 2 legs.