What does how many mean in math

Np4=12np2 with clear explanation.

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.

Siri can type 90 words in 40 minutes about how many words would you expect her to type in 10 minutes at this rate