Please can anyone help me to solve this problem? This problem (b) is to find E, V and C(capacitantce) in some dielectric materials. But I could’t understand the solutions about (b)

Solution manual says that the total surface charge density of (b) is +σ in upper plate. so it equals to E and ε_0V/d. But it seems wrong. +σ is not talal charge density but free charge density. isn’t it? I mean

σ_total=σ_free+σ_bound=σ + σ_bound

I wonder if I thought wrong. It would be appreciated when someone help me.

ps: I attached the problem and solution

I didn’t write in the form that PF gives, because my question is very simple.

http://ift.tt/1kKNy4k