The pKa of HN3 is 4.7. What is its Ka? Use a scientific calculator

Ka is the equilibrium constant for the dissociation reaction of a weak acid. A weak acid is one that only partially dissociates in water or an aqueous solution. The value of Ka is used to calculate the pH of weak acids. The pKa value is used to choose a buffer when needed. Choosing an acid or base where pKa is close to the pH needed gives the best results.

Where is the following?

Ithink that the use of creativity in the sciences entails that one produce something out of nothing or from another thing. with this, i think that the he wrote down his results as four parts of the atomic theory is the manifestation of the  creativity of john dalton.