First of all, as you seen the gases are noble which means that will not react with each other and in this case each gas create individual pressure.
P= total pressure
P = pressure of neon
P = pressure of argon
P = pressure of helium {which is required}
P = P
+ P
+ P
1.25 = 0.68 + 0.35 + P
P = 1.25 - [0.68 + 0.35] = 0.22 atm
The volume of copper : 3.24 ml
<h3>Further explanation </h3>Density is a quantity derived from the mass and volume
Density is the ratio of mass per unit volume
With the same mass, the volume of objects that have a high density will be smaller than objects with a smaller type of mass
The unit of density can be expressed in g/cm³ or kg/m³
Density formula:
ρ = density , g/cm³ or kg/m³
m = mass , g or kg
v = volume , cm³ or m³
A common example is the water density of 1 gr / cm³
The density of copper : 8.96 gr/ml
mass of copper : 29 g
then the volume :