[tex]\qquad\qquad\huge\underline{{\sf Answer}}[/tex]
According to Charles law, if pressure remains constant, volume varies directly with temperature. so we can infer that :
[tex] \qquad\sf{\dfrac{V_1}{T_1}=\dfrac{V_2}{T_2}} [/tex]
So, we can use this formula to find out the final temperature of the gas ~
Note : Take temperature in Kelvin ( 100°C = 373 K )
[tex]\qquad \sf \dashrightarrow \: \dfrac{3}{373} = \dfrac{6}{x} [/tex]
[tex]\qquad \sf \dashrightarrow \: x = \dfrac{6}{3} \times 373 [/tex]
[tex]\qquad \sf \dashrightarrow \: x = 2 \times 373[/tex]
[tex]\qquad \sf \dashrightarrow \: x =74 6 \: K[/tex]
Now, convert it to Celsius ~
i.e 746 - 273 = 473° C
So, the final temperature of the gas will be equal to 473° C
