since
density = mass/volume (which is just another word for size)
density of cube X = (cube X's mass) / (cube X's volume)
lets name "(cube X's mass) / (cube X's volume)" as "x"
density of cube Y = (cube Y's mass) / (cube Y's volume)
lets name "(cube Y's mass) / (cube Y's volume)" as "y"
then to calculate how many times is the density of cube X to density of cube Y, then it will be x/y
if calculating how many times greater, then it is (x-y)/y
though the phrase "how many times greater" can also mean "how many times".
