Convert 5.74x10^8 to standard form

Can someone me with 3 and 4 plz. this is for masteries test.

What are the two largest greenhouse gases

Harry lives in a city, and he has a lung condition known as asthma. on certain days, harry has to stay inside because pollutants in the air make it difficult for him to breathe. which of these pollution sources are nonpoint sources that might bother harry if he goes outside? choose the two that apply.