6. A study was conducted to determine whether the mean braking distance of four-cylinder cars is greater than the mean braking distance of six-cylinder cars. A random sample of 20 four-cylinder cars and a random sample of 20 six-cylinder cars were obtained, and the braking distances were measured.  

(a) What would be the appropriate hypothesis test for this analysis? 

(i)   t-test for two independent samples 

(ii)  t-test for dependent samples 

(iii)  z-test for population mean 

(iv)  correlation 

(b) Explain the rationale for your selection in (a). Specifically, why would this be the appropriate statistical approach?