Does this look familiar?

$\large \int_{-\infty}^{\infty} \left( \dfrac{e^{\frac{-x^2}{2}}}{\sqrt{2\pi}} \right) dx$

If the value for the above integral is $A$ , find the value of $b$ such that

$\large \int_{-b}^{b} \left( \dfrac{e^{\frac{-x^2}{2}}}{\sqrt{2\pi}} \right) dx = 0.9A$ .

Give the answer to the nearest 3 decimal places.