$\text{If Intensity of each wave is I then } I_0 = 4I$

$ \text{ At a point which is equidistant from slit the phase difference due to path difference is zero}$

$ \text{Net path difference at such point is } \frac{\pi}{3}$

$ \Rightarrow I_{net} = I + I +2I cos \frac{\pi}{3} = 3I = \frac{3I_0}{4}$