Implement the desired_marketing_expenditure function, which returns the required amount of money that needs to be invested in a new marketing campaign to sell the desired number of units.

Use the data from previous marketing campaigns to evaluate how the number of units sold grows linearly as the amount of money invested increases.

For example, for the desired number of 60,000 units sold and previous campaign data from the table below, the function should return the float 250,000.

Previous campaigns

Campaign	Marketing expenditure	Units sold
#1	300,000	60,000
#2	200,000	50,000
#3	400,000	90,000
#4	300,000	80,000
#5	100,000	30,000