A buffer solution of volume 50.0 mL contains 12.5 mmol HNO2

A buffer solution of volume 50.0 mL contains 12.5 mmol HNO2 and 9.25 mmol KNO2.A. What is the pH of this solutionB. If 1.00 mmol of Ca(OH)2 is added to the solution what will be the new pH?C. if 2.00 mL of 2.00M HCL is added to the original solution what will be the new pH?* I need to see all the work done to obtain the correct answer even the smallest calculation including mmol to mole and so on. Including every detail of how each step is taken will help me learn.