Example reaction between RBr and HO

The initial rate of reaction between an alkyl bromide and HO- was measured as a function of the initial concentrations of the reagents, with the following results [8]  

Taking logarithms, log r0 = log k + a log [RBr]0 + P log [HO ]o, and using the data in the first two columns (for which [HO 0 is constant), we obtain a pair of simultaneous equations from which we calculate a = 1.0. Then, from the second and third columns (for which [RBr]0 is constant), we obtain two other simultaneous equations, from which we 

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