Answer:
AC = 4DB
Step-by-step explanation:
see attachment
Given that B is the midpoint of AC, this means that AB≅BC.
Also, D is the midpoint of AB, therefore AD≅DB.
This shows that AD is 1/4 of the length of AC, since it is 1/2 of the length (1/2 x 1/2 = 1/4). DB is the same length, since it is congruent to AD.
Thus, AC = 4DB.