chemistry help please?

I got the answer for both problem but dont know how to do them help please step by step if possible need this for a test. Calculate the pH of the following: a. 0.500 M H2CO3 :answer is 3.33 b. 0.0325 moles of NaHC2O4 is added to 100.0 mL of 2.00 M H2C2O4: 0.46