How do you get the mass with volume and no density?
Well, you could always just put it onto a scale to find the mass. But assuming you aren't talking about a laboratory setting...
The general formula is:
#\mathbf(rho = m/V)#
#rho#is density in #"g/mL"#if mass #m#is in #"g"#and volume #V#is in #"mL"#.
So to get the mass...
#color(blue)(m = rhoV)#
Or to get the volume...
#color(blue)(V = m/rho)#
When you have the volume and not the density, and you want to find mass, you will need to find the density yourself. It's often readily available on the internet.
Just replace "[...]" with the object you want, and if it's not exactly what you need, consider it an estimate.
These days, you should be able to search for the density of any common object.
When you have the density and volume but not the mass, then just make up a mass.
You shouldn't need specific numbers to do a problem. You can always solve a problem in general and get a solution formula. If you need to, just make up some numbers that you know how to use.