Calculate the pH of 0.025M Formic Acid using pKa

Calculate the pH of 0.025M Formic Acid (pKa=3.75) and 0.05M Sodium Formate?

Could you explain step by step.

Thanks so much in advance!

You have made a formic acid / sodium formate buffer.
The pH of the solution is calculated using the Henderson - Hasselbalch equation:
pH = pKa + log ([salt] / [acid])
pH = 3.75 + log ( 0.05/0.025 )
pH = 3.75 + log 2
pH = 3.75 + 0.30
pH = 4.05