Grouping data by defined time periods

Hi

I have a report which shows the no of days between a quote being sent and an order being received. I have used a formula which subtracts quote reply date from order received date.

I want to group the data in the report so that i can see the orders that were recieved within 2 weeks of quoting, then the orders that were recieved between 2-4 weeks, then 4-6 weeks, then 7-10 weeks, then 10 plus.

I also want to try and display the data on a pie chart to show the percentage of orders which were recieved in each time period.

I am sure it should be fairly simple but i can't find a way of doing it.

Report attached for reference

Thanks.