Aconcrete stepping-stone measures 20 square inches. what is the area of 30 such stones?

When y’all answer can y’all explain too !

Awater holding tank measures 105 m long, 50 m wide, and 8 m deep. traces of mercury have been found in the tank, with a concen- tration of 60 mg/l. what is the total mass of mercury in the tank? answer in units of kg.

How long must $542 be invested at a rate of 7% to earn $303.52 in interest? in a easier way