hypothesis testing/Critical Region, must i find μ or XBar?

ok guys, im not askng you to do my homework, but i could use a point in the right direction..

ive got one of those fun filled packets where each question depends on the previous answer, so if i start it right i should be ok..

Background - many studies over the years have established "normal" levels of red blood cells and hemoglobin in children. The distribution of hemogloben levels is approx normal and the middle 95% of "normal" children have levels between 11 and 16 grams per deciliter of blood, That implies that the standard deviation of "normal" level is approx σx=1.25

Let X represent a random value taken from a randomly chosen child.

State a null and alternative hypothesis that would be appropriate for a health examiner to examine.

So far, i'm assuming that my H0 would be H0:X≥11, H1:X<11..now this is just a simple dumb question, but is X the right value/terminology to use in my hypothesis?

Now the rest of the packet is basically draw the distribution of XBar, from a sample of n=100..show rejection regions....and at the very VERY end it says calcualte the errors of β

Im a bit confused if i need to actually find Xbar/mew to do this or not..umm im sure part of it is im not interpreting this correctly. I only ask this because every formula i see requires XBar and mew.

Any help/pointers is appreciated, thanks in advance.