The solution equals to their concentration in pure water

Question

1. Determine the concentration of water, in mol/L, in a watery diluted solution, at room temperature. (Assume that their concentration in the solution equals to their concentration in pure water)

2. Copied from the assignment:
     (a) k_a =[H⁺] [A^-] / [HA]

     (b) logk_a =log[H⁺] + log{[A^-] / [HA]}

It's customary to write down the letter p before a factor in order to define it this way:

          pX =-logX

     (c) pH = pk_a +log{[A^-] / [HA]}

Write down the different stages that went from equation (b) to get equation (c)