It will take 5 months and the payments will be as follows:
Month 1: $375 to Mini and $3.15 to Murk
Month 2: $375 to Mini and $3.15 to Murk
Month 3: $165.58 to Mini and $209.42 to Murk
Month 4: $375 to Murk
Month 5: $87.36 to Murk
The z-statistic can be calculated as the difference in the population mean and sample mean divided by the standard error. The standard error can be calculated as the standard deviation divided by square root of sample size. The standard error:
SE = 12/ sqrt(20) = 2.68
The z-statistic: (195 -208) 2.68 = -4.86