Thermodynamics · Gibbs energy and equilibrium constant

In a closed flask at 600 K, one mole of $\ce{X2Y4(g)}$ attains equilibrium as given below:

$\ce{X2Y4(g) <=> 2XY2(g)}$

At equilibrium, 75% $\ce{X2Y4(g)}$ was dissociated and the total pressure is 1 atm. The magnitude of $\Delta_\mathrm{r}G^\ominus$ (in kJ mol$^{-1}$) at this temperature is . (Nearest Integer)

(Given: $R = 8.3$ J mol$^{-1}$ K$^{-1}$; $\ln 10 = 2.3$, $\log 2 = 0.3$, $\log 3 = 0.48$, $\log 5 = 0.69$, $\log 7 = 0.84$)