Gc. what sample size is needed so that the length of the interval is $60 with 95% confidence?

What sample size is needed so that the length of the interval is $60 with 95% confidence?  We Assume:   σ      =     $150.

Showing Work:

n   >  is the sample size we want to find:

N        =      ( z  a/2^σ / E )^2

=               ( 1.96   *     150 / 30 )^2        (margin of error is 1.96 times the standard error):

 >      96.04   ≈     97

Hope that helps                                        : )

the answer is b