A gas is in a cylinder with a piston. Its pressure is halved while its temperature rises from 300 K…

Step 1. The cylinder. $\lambda$ is proportional to $\dfrac{T}{p}$. The temperature grows by $\dfrac{450\ \text{K}}{300\ \text{K}} = 1.5$ and the pressure falls by a factor of 2. So $\lambda$ grows by $1.5 \times 2 = 3.0$.

Step 2. The sealed box. $\lambda = \dfrac{1}{\sqrt{2}\,\pi d^2 n}$ depends only on $n$ and $d$. Neither changes. The factor is $1.0$.