How to use COUNTIF only if certain conditions are met

Thank you Philip.  Not homework, but real work.  I made it work with the formula.  Your pivot table just added all the classes x or not.  There is one more item.  I thought that I could figure it out with the information you gave me, but no.  There is another column - Times taught.  I need to multiply that number with the Class length column.  Can I do this on the fly or do I need to have a hidden column that does this and pick up the number from that column?  I've attached the worksheet with the new column.