And here's the guide of how to solve:

When [Hg2+] = 1.14 M, the observed cell potential at 298 K for an electrochemical cell with the reaction shown below is 2.147 V. What is the Mn2+ concentration in this cell? Hg2+ (aq) + Mn(s) Hg() + Mn2+ (aq) [Mn2+] = mol/L Step 1 Decompose the cell reaction given into half-cell reactions and look up the standard electrode potentials. Step 2 Use these to calculate the standard cell potential: Ecell - Ecathode - Panode Step 3 Determine the value of the reaction quotient, Q, using the value of cell and the measured value of Ecell- At 298 K. 0.0257 V Ecell = Eco In Q Step 4 Calculate the unknown concentration using the values of Q and the known concentrations