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 freshmen can be arranged in 4! = 24 ways as a group
And they can be placed (as a group) in 4 ways in the line
And for each of these arrangements, the sophomores can be arranged in 3! = 6 ways
So
24 * 4 * 6 =
576 arrangements
+819 
