Answer
$[H^+] = 3.4641 M$;
$[OH^-] = 3.4641 M$.
Work Step by Step
1. Because it is a neutral solution:
$[H^+] = [OH^-]$
2. Multiplicating the concentrations of [H+] and [OH-], we obtain $K_w$.
$[H^+] \times [OH^-] = K_{w}$
$[H^+] \times [OH^-] = 1.2 \times 10^{-15} $
3. For math purpose, let's call [H+] by [OH-], because they have the same value.
$[H^+] \times [H^+] = 1.2 \times 10^{-15} $
$[H^+]^2 = 1.2 \times 10^{-15} $
$[H^+] = 3.4641 \times 10^{-8} $ M
4. Because [OH-] = [H+]:
$[OH^-] = 3.4641 \times 10^{-8} $ M
