Please show the Excel formulas! Linda is $10$ years old. Her parents want to save for $4$ years of college, starting at $18.$ Her parents want to deposit X today and on birthdays $11,12,....17.$ On birthdays $18,19,20,21$ they plan to take out $$20,000$ the total cost of education $(18-21$ is $$5,000$ for those years, not $$20,000$ each year.$).$ How much do her parents need to save each year? Assume the discount rate is $10\%.$ Solve the following ways:

a$.)$ Using trial and error, is the $$4,000/$per year enough?

b$.)$ Using Goal Seek, solve for the annual deposit necessary to meet their financial goals.