Answer: Two.
list hhid if race == 3 & age == 50
This one was a bit tricky. The above command displays the value of the variable hhid for all observations with a race value of 3 and an age value equal to 50. Considering all you want to know is the raw number of individuals, any variable could be put in the place of hhid. Try this again, although instead of using the hhid variable, use the variable hhsizem. While the value displayed in the STATA Results window has changed (with hhid the values 64012 and 145055 were displayed - representing the unique identification numbers given to these individuals' households, with hhsizem the values 4 and 7 were displayed - representing the number of individuals in the each person's family respectively), the number of observations has not, there are still only two observations displayed.