Calculate Difference on Time

Good day, everyone,

I have made the following Excel table:

I would like that the table would do the following:

After the entry in "Entry", I would like that the column "Last" finds the latest entry before the current, and in column C, calculate de difference between the dates. 

Example: I have 4 entries now. 

A3 has July 21; that way B3 would calculate the contents of the latest entry before July 21, which would be July 18, and calculate the difference between the dates – i.e. 3 in C3.

Thank you.