Populate Column With Later Dates

I am trying to find a formula that will automatically populate two columns on the same worksheet that a date is being entered in a different column. We train 468 new bus drivers every year and to accomplish this, we run 26 classes of 18 students with a new class starting every two weeks at our training facility. Each class is in training for six weeks (30 working days). The first 19 days they are under the instruction of our full-time instructors. The next nine days they are out on ‘line instruction’ with regular drivers. On days 29 and 30 they are back in the training department for final evaluation and graduation. On Day 31 they are turned over to Service Delivery as regular full-time drivers.

If I enter a class start date of April 6, 2009 in cell B4 on "2009 Conventional Classes", the formula would automatically fill in D4 and E4 columns with dates that are 29 days later and 31 days later respectively but, would skip weekends and any statutory holidays (these would be represented by a different background color on the calendar templates).