You can find the pH by taking the negative log of the concentration of H+ or H3O+ and the pOH by taking the negative log of the OH-
There are various ways to do calculations with Ka and the pH.
We checked out Bronsted-Lowery acids and bases and the theory with proton donors/acceptors.
Also, with chemistry, you want to be very careful with the names since changing them slightly can mean a different substance.
And rounding early is not a good plan since it can introduce inaccuracy.