Initial volume is 2.3l, initial temperature 150°c and initial pressure 2.5atm. temperature increases to 300°c and pressure doubles. the new volume is?

This is using the Combined Gas Law, which is the following:

, or 

Since you are solving for , you can change the equation to be:  =

Your given values are as follows:
: 2.5atm
: 2.3L
: 150°C
: 5atm
: 300°C

This formula only works if temperature is given in terms of Kelvin, so you can convert 150°C and 300°C to Kelvin by adding 273. Doing this, you get the following values:

=423K
573K

You then plug in all of the values you are given to get:

= 

Multiply/divide all of the values to get:

= 0.85L rounded to the nearest hundredth