Algebra-1

After marrying with Ana, biologist Mendel found it was difficult to maintain the marriage, so to avoid his wife, he spent the whole day in the lab. One day he was studying two species of bacteria. The number of species A is 3 times than that of species B. After 3 hours, the total number of bacteria from both species is 4000. How many bacteria of species A were there after 3 hours?