I hope someone can work out this problem for me to use as a reference for my homework. Thank you so much in advance.

The length in centimeters if n=29 fish yielded an average length of x=16.82 (i don't know how to put the line over the x) and $\displaystyle s^{2}=34.9$. Determine the size of a new sample so that x(+/-)0.5 is an approximate 95% confidence interval for $\displaystyle \mu$.