Asample of nitrogen gas has a pressure of 7.58 kpa at 639 k. what will be the pressure at 311 k if the volume does not change?

This problem is dealing with an ideal gas.  Given that it is ideal we can proceed the solution using the formula: PV=nRT. The statement says "the voluem does not change", this means that our V is constant. Assuming that the gas is inside a close container the number of moles, n is constant as well. Manipulating the equation where all constants and variables are on different sides: 

P/T = nR/V

Solving: 

7.58kPa/639 K = x/311K

x = 3.69 kPa