To be able to calculate the monthly salary of an executive in an engineering firm, here are the steps:
1. Subtract the Christmas Bonus of $7,000 from the total earnings per year. This is because Christmas Bonuses only happens once a year, not every month.
2. Divide the result in #1 by 12 months since there are 12 months in a year.
Therefore, an executive in an engineering firm earns a monthly salary of $6, 691.67.