A stock of potium dichromate solution K2Cr2O7, Calculate molartiy of solution , please Help?

A stock potium dichromate solution K2Cr2O7: molar m is 294.2 g/mol) is prepared for dilution by dissolving 25.0 grams of K2Cr2O7 in a 500.0 ml volumetric flask. then, 15.00ml of the stock K2Cr2O7 solution is placed in a flask and diluted to a final volume of 100.00 mL. Calculate the molarity of the solution , please help , I HAVE no idea where to start!!