J.R. S. answered 04/05/21
Ph.D. University Professor with 10+ years Tutoring Experience
Assuming the base is a strong base which ionizes/dissociates completely, the [OH-] = 0.026 M, since
BOH => B+ + OH-
0.026 M....0.026 M..0.026 M
You should also know that [H3O+][OH-] = Kw = 1x10-14.
[H3O+] = 1x10-14 / 0.026
[H3O+] = 3.8x10-13 M