Can you make this (office stop charges $15.99 per pack but is offering 10 packs free if you purchase over 50 packs.) in to an equation

On a piece of paper graph f(x)=5•(0.4)^x

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

3.4a=57.8 what is the the value of a