I know that p=m/v but I still have no idea how to answer this word problem:

"b) Calculate the density of a mixture of 40% antifreeze and 60% water, if there is a 5% decrease in total volume when they are mixed."

and just in case this question needs the previous question since they are both part of the same number, here is the previous question (which I figured out how to do):

"a) Calculate the mass of a four-litre jug of antifreeze (ignore the mass of the plastic container) if the density of antifreeze is 800 kb/m^3."