An average person in the united states throws away 4.5 × 10^–1 kg of trash per day. in 2013, there were about 3.2 × 10^6 people in the u. s.
about how many kilograms of trash was thrown away in the united states in 2013?
5.3 × 10^? kg

Multiply 3.2*10^6 and 4.5*10^-1 to get 14.4*10^5, or, expressed more properly, 1.44*10^6.  This is the amount of trash thrown away per day.  To get the amount thrown away in 2013, multiply by 365 to get 1.44*10^6*365=525*10^6, or 5.25*10^8.