Use PV=nRT. Rearrange the variables to get T on one side, then simply plug in your variables. P is pressure, V is volume, n is the number of moles, R is the gas constant (0.082 L·atm/mol·K), and T is the termperature. Note that T will be in Kelvin, so you may have to change it depending on the requirements of the problem.
To find the temperature of the gas, you can use the ideal gas law equation: PV = nRT. Plug in the values given: P = 1.5 atm, V = 11.4 L, n = 0.49 mol. Convert pressure to atm if necessary. Solve for T to find the temperature of the gas.