When 300 J of heat given to an ideal gas with C_p=7/2 R its temperature raises from 20^° C to 50^° C keeping its volume constant. The mass of the gas…

When $\displaystyle 300$ J of heat given to an ideal gas with $\displaystyle C_p=\frac{7}{2} R$ its temperature raises from $\displaystyle 20^{\circ} \mathrm{C}$ to $\displaystyle 50^{\circ} \mathrm{C}$ keeping its volume constant. The mass of the gas is (approximately) $\displaystyle \_\_\_\_$ g. $\displaystyle (\mathrm{R}=8.314 \mathrm{~J} / \mathrm{mol} . \mathrm{K})$