I’m confused how do you know where to put the plus and minus signs when rearranging the equation?

Can some one me with these questions

What is mean median mode and range?

An observer(o) spots a plane(p) taking off from a local airport and flying at a 29 degree angle horizontal to her line of sight and located directly above a tower(t). the observer also notices a bird circling directly above her. if the distance from the plane(p) to the tower(t) is 6,000ft., how far is the bird(b) from the plane(p).