Show open cases over time by parameters

Here's my problem.

I have a table that shows information requests with the following columns:

REQUEST TABLE:

Office {Finance, Marketing, Design}

Contractor {Primary Contractor Name)

Request Date (Date)

Reply Date (Date)

I want to make a graph showing how many requests are open at any one time and allow someone to filter on Office and Contractor as well as date.

I've loaded a calendar with every date over the applicable timeperiod.

I've also ripped this into 2 different tables - one showing requests and the other showing closes.  What I want to show is the increasing backlog over time.

Any help would be greatly appreciated.