Need help with random mc

Im working on a game that is going to be a shootemup.
Its going to be a canon(helicopter) in the top that shoots at diffrent targets that are on the ground scrolling by so you get the feeling that the helicopter is flying. Got a problem with the targets…
How do I write the code 4 a mc to be random placed under 280 pixels in the Y cordinate.
Its probably pretty simple but Ive tried too figure it out but I cant get it right.
It would be great if someone could help me out here! :ponder: