If Janice was 21 years old z years ago and Lisa will be 19 years old in p years, what was the average (arithmetic mean) of their ages 8 years ago?  Choose the correct option
A) (z + p)/2  B) (z - p + 24)/4  C) (z - p + 14)/4  D) (z + p + 34)/2  E) (z - p + 24)/2
Today, J = z+21 and L = 19-p   8 years ago, J = z+13 and L = 11-p   The average of their ages was (z-p+24) / 2   The answer is (z - p + 24)/2.
<result>E</result>
If Janice was 21 years old z years ago and Lisa will be 19 years old in p years, what was the average (arithmetic mean) of their ages 8 years ago?