What mass error (in mg, round to the nearest tenth) would occur in the weighing of 450 mg of a drug if the uncalibrated balance created a 15 % error in all measurements?

The mean finish time was 185.52 with a standard deviation of 0.327 minute. the winning car driven by chris finished in 185.13. the previous year race had a mean finish time of 110.3 with a standard deviation of 0.106. the winning car that year driven by karen finished in 110.13 minutes. find their respective z-scores. chris - z-score karen “- z-score