Acid concentration Q's

[dcl]

Heya's
Having some problems with the following question:

Trimethylacetic acid C_4 H_{11} COOHis a weak monoprotic acid. When 0.0010 mol of Trimethylacetic acid was dissolved in 100mL of water, the concentration of trimethylacetic ion was found to be 3.0 \times 10^{ - 4} mol.L^{ - 1}

a) What is monoprotic acid?
An Acid that donates only one proton.

b) Use the above data to work out pK_a for Trimethylacetic acid.
now pKa = -log[Ka] think? How would I go about working Ka out?

c) What volume of 0.2M KOH would be required to neutralise this solution of trimethylacetic acid?
For this I would just work out how many moles are in the 100mL solution, and then use that to work out how how much volume of KOH I would need to add.
However I'm unsure how to work out how many mols are in the 100mL solution, It's an easy units conversion problem im sure, but I suck at it :(

[thunderfvck]

Look at the concentration of the ion.

If there's that much in the solution that exists as an ion, an equal amount must exist as H+.

[Gokul43201]

Ka= \frac {[H^+][A^-]} {[HA]}

and

[H^+] = 10^{-7} + [A^-]