74. Solving a chemistry problem

6. The EMF of a cell containing Br-ISE in a wastewater sample prepared for analysis with an ionic strength of 0.1 mol/l is equal to Ei=230 mV. After adding 6.78 ml of a solution of 5 * 10-3 MKVg to 25 ml of this solution, containing 0.1 mol/l KNO3 to maintain a constant ionic strength, the EMF of the cell was E2 = 203 mV. Calculate the concentration of Br-ions (g/l) in wastewater if Br-ISE has an experimental electrode function gradient O=55 mV/pBr.