Carry out the following operations as if they were calculations of experimental results, and express each answer in the correct units with the correct number of significant figures: (a) 7.310 km ã· 5.70 km (b) (3.26 x 10^-3 mg) - (7.88 x 10^-5 mg) (c) (4.02 x 106 dm) + (7.74 x 107 dm)

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.