Please help!!! I need the answers ASAP I have 40 mins to pass this

A 0.800 M solution of NH3 is prepared and is in equilibrium with its ions.
a.) What is the hydroxide ion concentration of the solution? Ammonia has a Kb of 1.75x10 − 5
b.) What is the pH of the solution? Ammonia has a Kb of 1.75x10−5.
c.) What is the percent of ionization? Ammonia has a Kb of 1.75x10−5.
d.) Is the assumption valid (using the 5% rule)? Ammonia has a Kb of 1.75x10−5.

What is the pH of a solution if the given is [OH−] = 4.5x10−4M?

choices:
9.10
7.52
10.65
3.35