A national firm reports mean earnings of $75 $12 ( ) per unit sold over the lifetime of the company. A competing company over the past 36 reporting periods had reported mean earnings equal to $78 per unit sold. Conduct a one-sample z test to determine whether mean earnings (in dollars per unit) are larger (compared to that reported by the national firm) at a .05 level of significance.

Compute effect size using Cohen's d.