Ok, I have got my Ho and H1 values.

I have got my t statistic by using

I am now being asked for the null distribution of this. I assume this means something in the form of a binomial or normal distribution - but this a t distribution right? So I am a little stumped as to what I am being asked.

I think I have done all the maths and working, but am having a little trouble putting names to the different parts of it.

After reading lots of books and Googling a lot, I cannot find many references to a 'null distribution'.