The simplified expression is 3/(y - 3).
First, we factor the denominator of the given expression as the difference of squares:
(y/3 + 1)/((y ^ 2)/9 - 1) = (y/3 + 1)/((y/3 + 1)(y/3 - 1))
Then, we can cancel the common factors in the numerator and denominator:
(y/3 + 1)/((y/3 + 1)(y/3 - 1)) = (y/3 + 1)/(y/3 - 1)
Finally, we can simplify the expression by dividing the numerator and denominator by y/3:
(y/3 + 1)/(y/3 - 1) = (y/3 + 1/(y/3)) / (y/3 - 1/(y/3))
= (1 + 1/y) / (1 - 1/y)
= (1y + 1) / (y - 1)
= 3/(y - 3)
Therefore, the simplified expression is 3/(y - 3).