Answer:
 1/2
Explanation:
You want the value of b/a when (a+1)/(b-1)=5/1 and (a-1)/(b+1)=1/1.
Solution
The latter equation tells you ...
 a -1 = b +1
 b = a -2
Then the first equation tells you ...
 a +1 = 5(b -1)
 a +1 = 5(a -2 -1) substitute for b
 a +1 = 5a -15 . . . . eliminate parentheses
 16 = 4a . . . . . . . . add 15 -a
 4 = a . . . . . . . . . divide by 4
 b = a -2 = 4 -2 = 2 . . . . find the value of b
 b/a = 2/4 . . . . . . . . . . find the desired ratio
 b/a = 1/2