We're dealing with a gas here, so keeping the Ideal Gas Law

pV = nRT

in mind, is a good idea

Since we're not interested in the type of gas, i.e. moles (so we don't need R either)
and the volume remains constant, pV = nRT we'll end up with

p = T, also called Gay-Lussac's Law

Kelvin

First, let's do a temperature conversion 27°C + 273.15 = 300.15 -173°C + 273.15 = 100.15 It is not really necessary to convert °C to K in this case, since both initial and final temperature has the same units, but it is good practice and proper form

Gay-Lussac's Law

Now, we can set up a ratio pinitial / Tinitial = pfinal / Tfinal adding provided data 6 atm / 300.15 K = p / 100.15 K

Celcuis

(6 atm)(100.15 K) / 300.15 K

= p

p = 2.00199 atm

The final pressure of this gas is 2 atm