Answer:
He wants to see if the proportion of the 125 tea-drinking employes is, as the newspaper report claims, 30%.
Then the null hypothesis says that this is false and that there is no relation between the events.
Then the null hypothesis is:
The proportion of all tea-drinkers at the company that prefer green tea to black the is not the 30%
Which is the negation of the thing that Leo wants to check.