How to know which formula to use for the electric field of a conducting plate of charge? $=σ/2ε_0$ or $=σ/ε_0$?

Question

I'm so confused right now as I have come across questions regarding the E.F of a conducting plate of charge.However some questions use =σ/2ε0 whereas others use =σ/ε0 and I genuinely don't know why and when to choose which.