Calculate the pH and pOH of each of the following solutions?

[H3O+]= 1.7×10−8 M

pH = – log 1.7 x 10^-8 =7.8
because [H3O+][OH-]= Kw = 1.0 x 10^-14
[OH-]= 1.0 x 10^-14 / 1.7 x 10^-8=5.8 x 10^-7 M
pOH = – log 5.8 x 10^-7 =6.2

in the same way
pH = 7.0
pOH = 7.0

pH = 5.7
[OH-]= 5.0 x10^-9 M
pOH = 8.3