Reapportionment Act of 1929 was passed in order to put in place a permanent method for dividing a constant 435 in the US house of representative in accordance with census. According to the constitutions, each state was supposed to have one representative in the house of representative. As the population of US increase, it becomes difficult how to choose members of house of representative, hence this law.
I'd say that the answer is observational study because they're just analyzing the data and if it were an experiment they'd be taking data and comparing it.
