How many significant figures are in the measurement 0.00004020 mg?

Transportation is the largest single source of air pollution in the united states. air pollution can harm the environment and human health. which technology could offer a solution to this problem? mufflers that reduce noise motors that run on electricity tires that improve gas mileage

Is laundry detergent an acid or a base?

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