How much of a 15.0 M stock solution do you need to prepare 250 ml of a 2.35 M HF solution?

nanotechnology is a powerful tool in biomaterials research as it creates numerous possibilities for the engineering of functional molecules. nano-bio refers to projected ability to incorporate biomimicry into various materials at nanoscale.  

a saline water is fed to a reverse osmosis unit at flow rate o rotameter connected to reject (retentate) line reads 8 installed in reject and permeate line reads 15.2 milli siemens/cm and 300 micro siemens/com respectively.