Triangle ACD consists of AC, AD and CD.
Because AD is the center line of triangle ABC.
So CD = BD
So the difference between the perimeters of triangle ABD and triangle ACD is 5-3 = 2 cm.
(2) Because the area of triangle ABD is 1/2*AE*BC.
The area of triangle ACD is 1/2*AE*CD.
And because BC=2CD.
So the area of triangle ABD is twice that of triangle ACD.