**Answer 1**

[OH-] = 2.87×10^-7M

pOH = -log[concentration]

pOH = -log [2.87×10^-7]

pOH = you figure it out. Between 6 and 7 if you did it right.

Your other questions are typed in poorly so I cant decipher what you’re truly asking.

**Answer 2**

[H3O+] x [OH-] = 1.00 x 10^-14

So, if you have one, just divide it from 1.00 x 10^-14 to get the other.

Taking the ‘a’ problem for example: (1.00 x 10^-14) / (2.87 x 10^-7) = 3.48 x 10^-8