Stout Electric Company operates a fleet of trucks that provide electrical services to the construction industry. Monthly mean maintenance cost has been $75 per truck.A random sample of 20 trucks shows a mean maintenance cost of $68.50 per month. It is also known that the population standard deviation is $30 . Managers want to determine whether or not the mean monthly maintenance cost has decreased. Use a .05 level of significance.Stout Electric Company operates a fleet of trucks that provide electrical services to the construction industry. Monthly mean maintenance cost has been $75 per truck.A random sample of 20 trucks shows a mean maintenance cost of $68.50 per month. It is also known that the population standard deviation is $30 . Managers want to determine whether or not the mean monthly maintenance cost has decreased. Use a .05 level of significance.