If Janice was 23 years old z years ago and Lisa will be 21 years old in p years, what was the average (arithmetic mean) of their ages 7 years ago?  Choose the correct choice from the following choices.
A) (z + p)/2  B) (z - p + 30)/4  C) (z - p + 20)/4  D) (z + p + 40)/2  E) (z - p + 30)/2
Today, J = z+23 and L = 21-p   7 years ago, J = z+16 and L = 14-p   The average of their ages was (z-p+30) / 2   The answer is (z - p + 30)/2.
<result>E</result>
If Janice was 23 years old z years ago and Lisa will be 21 years old in p years, what was the average (arithmetic mean) of their ages 7 years ago?