Cations are removed from the exchange complex of a 1 kg oven-dry soil sample by ammonium (NH4+) substitution. The following masses of cations are removed from the sample: 1.51 g Na+, 1.56 g K+, 4.40 g Ca2+, 0.72 g Mg2+, and 0.05 g H+. What is the cation exchange capacity of the soil?