Backing up the shared drives

 Suppose you need to back up 50 TB of shared network drives frequently. Find the best solution using a backup tape technology. Compare to an external hard drive array solution.
 a) what are the costs of the two solutions, including media for 15 tapes for the first solution.(Provide the links for cost)
 b) how long would it take to back up the network drives for both solutions?(Provide links or calculations)
 c) which one would you select and why?