106. Solving a chemistry problem

For the bimolecular reaction of persulfate ion with bromide ion (S2O8Z Br- → products), the following dependence of the rate on ionic strength at 25 C was established:
I, mmol/dm3 2.45 3.65 4.45 6.45 8.45 12.45
k, dm3*mol-1s-1 1.05 1.12 1.16 1.18 1.26 1.39

Determine the rate constant at zero ionic strength and the charge of the persulfate ion, Z, from the charge of the bromide ion -1 (the charge of Z should be rounded to the nearest whole number).