As we know, resultant intensity is given by,
I=4I0cos2(2Δϕ) and phase difference can be written as Δϕ=λ2πΔx.
For first case:
I1=4I0cos2(λ2π×4λ)=4I0cos2(4π)=2I0
For second case:
I2=4I0cos2(λ2π×3λ)=4I0cos2(32π)=I0
Therefore, required value ofI0I1+I2=3.