# Maximum bending stress and neutral axis

I need to calculate the maximum bending stress

So let $$r$$ equal the radius $$\frac{1}{r} = \frac{M}{EI}$$ $$\sigma_{max} = \frac{Mc}{I}$$ $$\Rightarrow \sigma_{max} = E\frac{c}{p}$$

But how do I know where the neutral axis is?

The answers say it is $$\frac{c}{2}$$ which intuitively makes, but how can we come that conclusion in a more concrete manner?

I'm also confused to how you would find the second moment of area for this question should you do so?

$$X_n = \dfrac{x_1A_1+ x_2A_2 + x_3A_3 +\cdots}{A_1+A_2+A_3+\cdots}$$