How Much Time Must Be Saved to Justify a Lock-Box

How much time must be saved to justify a lock-box system that processes 350 checks per day at an average amount of $400 per check if the system will cost $20,000 annually and interest rates average 8%?

A) 0.56 days
B) 1.79 days
C) 2.14 days
D) 7.00 days