Chemistry bullshit

Okay... this is annoying. My prof gave me a problem with (I believe) a few different ways of balancing.

The Kb for the base urea ((NH2)2)CO is 1.5 x 10^-15. Calculate the pH of a 1.25 M urea solution.

I imagine it dissociates as so...
2NH3(g) + CO2(g) -> (NH2)2)CO (aq) +H2O (l)

But then what?

The arrow goes the other way, ammonia and carbon dioxide do not spontaneously form aqueous urea.

pH = pKa + log[base]/[acid]

and pKa + pKb = 14