Using the definition of K_p we can set up an initial, change, equilibrium box (or ICE box). The important bits in the question are the fact that the tube is sealed and that it's under atmospheric conditions. The sealed tube indicates that the total moles of gas will not change and the pressure will stay constant since the temperature, volume, and total quantity of gas (moles) is kept constant. The atmospheric conditions is another way of saying the pressure in the tube is 1 atm or 760 mmHg and so on. For the sake of simplicity, I'll be using atm.
The set up for your ICE box will start with N_2O_4 having one atm of pressure and NO_2 having no pressure since none is present. The change will be -x for N_2O_4 and +2x for NO_2 since for every mole of N_2O_4 decomposed, two moles of NO_2 are produced so the will contribute to the partial pressure twice as much. The equilibrium partial pressures will be 1-x and 2x for N_2O_4 and NO_2 respectively. (The commas in the box is for spacing only)
,,,,,,,,,,,,,,,,,,,,,,P_(N_2O_4),,,,,,,,, P_(NO_2)
Initial ,,,,,,,,,,1 atm,,,,,,,,,,,,,,,0
Change,,,,,,,,,,-x,,,,,,,,,,,,,,,+2x
Equil.,,,,,,,,,,,,1-x,,,,,,,,,,,,,,,,,2x
K_p is similar to K_c in the aspect of setting up the rate quotient, use the chemical formula with partial pressures of products (each raised to the power of their own coefficient) over reactants (also raised to their powers) using the equilibrium partial pressures. Then solve for x.
K_p=((P_(NO_2))^2)/(P_(N_2O_4))
0.14=(2x)^2/(1-x)
4x^2+0.14x-0.14=0
x~~0.170
From here, you can get the partial pressures of the gasses and use them to run a couple idea gas law equations
PV=nRT
(T is in kelvins not Celsius. Kelvins=273.15+celcsius)
Before you calculate for moles at equilibrium, you need to calculate the volume which can be done by using the initial gas, N_2o_4. (I'm still using atmospheres)
(1 )*V=(.1 )(O.0821)((273.15+25)
V~~2.45 L
Now with the calculated volume, you can use the partial pressures from equilibrium and run the ideal gas law, solving for n
n=(PV)/(RT)
n=(P_(N_2O_4)V)/(RT)
n=(P_(NO_2)V)/(RT)