Answer:
let X be the number of ways they can be seated without condition,
let M the the number of ways they can be seated if the two people must sit together,
let N be the number of ways they can be seated if the two must not sit together.
X=7! =5040
M= 6!× 2!=1440
M+N=X
then N=X–M=5040–1440=3600ways
