What is the [OH-] in a solution that has a [H3O+]=5.0 x 10-2 M?

What is the [OH-] in a solution that has a [H3O+]=5.0 x 10-2 M?
2.0 x 10-12 M
5.0 x 10-2 M
1.0 x 10-12 M
2.0 x 10-13 M
1.0 x 10-14 M