Calculating probability given mean and standard deviation

Hi I have looked around for this post on the forum but could not find one and have spent a while attempting this question:

Given that X is normally distributed with mean 100 and standard deviation 9 and given a sample size of 16, compute the following:

1) mean and variance of X-dash
2) P ( X-dash <= 98 )
3) P ( X-dash > 103 )
4) P ( 96 <= X-dash <= 102)

where X-dash is the sample mean.

My attempt so far:
I have used the formula

z = (X-dash - u) / (stdev(X-dash))

X ~ N(u=100, s^2=9^2) and,
X-dash ~ N(u=100, s^2=81/16) <-- not sure about this one

and Since I am not sure about the variance of X-dash I can't continue to work out the appropriate critical values for z from the tables.

Help please with as much detail in the solution as possible so I can follow.