(A) In another experiment also carried out at 298 K, equal concentrations of [Cu⁺], [Sn⁴⁺], and [Sn²⁺] are found to be in equilibrium. What must be the equilibrium concentration of [Cu²⁺]?

(B) At 25 °C, K = 9.14 x 10^-6 for the reaction 2 Fe³⁺(aq) + Hg₂²⁺(aq) ⇌ 2Fe²⁺(aq) + 2 Hg²⁺(aq). If the equilibrium concentrations of Fe³⁺, Fe²⁺ and Hg₂²⁺ are 0.015 M, 0.0025 M, and 0.0018 M, respectively, what is the equilibrium concentration of Hg₂²⁺?