First, convince us this isn't a homework assignment.
Second, are you an engineer? If you are then you will know which automatic calculator available on this site to use.
Third, also if you are an engineer you will know what piece(s) of critical information you left out.
Lastly, if you aren't an engineer and the failure of this structure could possibly in any way have any affect on human safety, then get in contact with an licensed engineer familiar with your local codes.