A speech class has $4$ freshmen and $3$ sophomores. (Everyone is distinguishable.) In how many ways can they stand in line, so that all the freshmen are standing together?

The sophomores can occupy any of 4 positions

And the can be arranged in 4! = 24 ways

And for each of these the sophomores can be arranged in 3! = 6 ways

So

4 * 24 * 6 = 576 ways