How can an isotope like carbon 14 be used to date dead organisms

  Hello there!
Carbon-14 is a radioactive isotope of carbon that is also organic. It Is in a constant value throughout our lives, and does not decay while within a living organism. Thus it decays just like any radioactive elemental isotopes does. 
So you can use that to date a dead organism based on the carbon 14 because carbon 14 does not Decay.

Mass of water is smething that you froma drug test or sum girl ya

Adozen is 1221/12 = 1.751.75 x 12 = 21therefore, 1.75 is the answer.