Hi, we would have to use process of elimination here. We can automatically knock out d and e since Dave can never be in 1.
We can knock out C because if those four fly together, then only a and d are left, but this is not valid since a and d cannot go together, and d would need to fly with a pilot. So, c can't happen.
We can also knock out A since it takes up all three of the pilots, which would leave d and e without a pilot, which is invalid.
