I honestly have NO idea on how to go about this calculation, it appears simple but I'm struggling, can somebody kindly go through the steps with me as I REALLY want to learn this!!

What is the Ratio of [Base]/[Acid] in the following Buffer system?

Information:

Target pH = 9.89

AB Pair = NH4Cl/NH3

pKa = 9.25

[NH3] > [NH4Cl]

[NH4Cl] = 0.10 M

5.35g NH4Cl Required

I have no idea on where to go from this information so could somebody please show me? I'm not that skilled in mathematics so please explain it properly, thank you