Preparing a 0.030 M solution of potassium ferrocyanide trihydrate?
It is quite trivial. Just calculate how many moles of potassium ferrocyanide trihydrate you need to measure out (n = C x V), then multiply with molar mass to see how many grams you need to measure out. After measuring the sample on analytical balance, quantitavely transfer it to the volumetric flask. Add some water and dissolve the sample. After homogenizing the solution, add water carefully to the full mark. You can't actually calculate the exact molarity of the prepared solution: you need to determine it experimentally, by performing a standardization with silver-nitrate standard using chromate salt as an indicator.