Question 970216
. 
J=Joanna's age; B=Betty's age=J+6yrs; M=Mary's age=J+2yrs
J+B+M=J+(J+6yrs)+(J+2yrs)=3J+8yrs
J=x
Sum of ages=3J+8yrs Substitute for J.
Sum of ages=3x+8 yrs