Answer:
609638400
Explanation:
Each row must alternate boys and girls, so every row is either BGBGB or GBGBG, where B denotes a boy and G denotes a girl. Since there are 8 girls and 7 boys, the teacher must have two rows of GBGBG and one row of BGBGB. There are three ways to choose this row, and once this is done, every seat is reserved for either a girl or a boy. There are 8! ways to arrange the girls in their seats, and 7! ways to arrange the boys, so the total number of seating arrangements is 3 * 7! * 8!