Homework Help: Time dilation

1. The problem statement, all variables and given/known data

At what speed does a girl need to travel, if her journey begins in 2009 and she wants to come back two years older in the year 2018.

^^^Can someone please check my answer. I am new to the topic

2. Relevant equations

T = To / sqrt(1-u^2/c^2)

3. The attempt at a solution

T(earth) = 9 yrs
To(girl) = 2 yrs

9 = 2 / sqrt(1-u^2/c^2)

81 = 4 / 1-u^2/c^2

81(1-u^2/c^2) = 4

(1-u^2/c^2) = 4/81

- u^2/c^2 = 4/81 - 1

u^2/c^2 = 1 - (4/81)

u^2 = 77/81*c^2

u = .974996043 c