For the reaction
4NH3(g) + 3O2(g) -> 2N2(g) + 6H2O(g) ,
K = 10^80 at a certain temperature. Initially, all reactants and products have concentrations equal to 12 M. What is the approximate concentration of ammonia at equilibrium?
a. 3 M
b. 12 M
c. 18 M
d. 6 M
e. 0 M