How would you prepare 250 ml of a 6.0m nano3 solution from a 15m nano3 solution?

This is pretty simple actually :) You are going to use the equation M1xV1=M2xV2 
M stands for molarity and V is volume. Plug in the information you have, and then solve for the unknown using simple algebra.  You get 6.0M NaNo3 x 250mL= 15M NaNO3 x V2. Now solve for V2. Keep in mind that you will have to use stoichiometry to convert to liters instead of liters if your answer requires it. Hope this helps! :) 

Evaporation: this is when warmth from the sun causes water from oceans, lakes, streams, ice and soils to rise into the air and turn into water vapour (gas). water vapour droplets join together to make clouds! condensation: this is when water vapour in the air cools down and turns back into liquid water.