Question 66774
Sarah's age (S) exceeds Dana's(D) age by 16 years. 
S=D+16...................1
Four years ago,
SARA WAS S-4 YRS
DANA WAS D-4 YRS
 Sarah was twice as old as Dana was then.
S-4=2(D-4)
S-4=2D-8............SUBSTITUTING FROM EQN.1
D+16-4=2D-8
2D-D=12+8=20
D=20
 Find the present age of each.
DANA IS NOW 20 YRS
SARA IS NOW 20+16=36 YRS