Read the data census . RData which can be found on Canvas. Check That it has 74020 rows and 31 columns. Each row represents a census tract, and each column a variable that has been measured. Load the plyr library. (Hint: it will be very useful!) 1. (2 points} How many states are represented among the 74020 census tracts? How many counties? 2. (1 point) Columns 8 through 31 of the census data frame represent numeric variables, but columns 8 and 9 are not stored as such. These two are measured in US dollars: median household income (Med_HHD_Inc_ACS_E)9_13} and median house value (Med House value AC5 99 13). What are The classes of these columns? 3. (5 points} Convert columns 8 and 9 into numbers (in whole US dollars). For example, $53 , 838 should be converted into the integer 63838. (Hint: you may first convert them into strings, then remove any non-numeric characters using substr( ) or gsub ( ) , then