Clear a cell when inputting data in a different cell

Hello,
I have a dual thing to do on a spreadsheet. I would like to put a date in one column (lets call it cell A1) which would in return put another date in a separate column but it would be dated 30 days ahead (let's call this cell A3).
Then, then I put a date in a totally different column (cell A2), it would clear the cell that has the 30 day future date (Cell A3).
I want to be able to do this in several rows, approx 200. What formula in VB would I use for all of this?
HELP!!!!