Purchasing factory equipment on credit results in a

Other things the same, a decrease in the price of a good will cause the

Jumbo, Inc. had sales of $8,000 in November, $14,000 in December, and projects sales of $10,000 in
January, $12,000 in February, and $8,000 in March. The firm's COGS in any given month is equal to 70% of the next month's sales. The firm collects its receivables in 60 days and pays its payables in 30 days.
The firm begins January 1 with $10,000 in cash. All sales and purchases are on credit. There are no other costs or revenues. What is Jumbo's cash balance at the end of March? Assume there are 30 days in every month.

The clearinghouse is:

Bill lives in Montana and likes to grow zucchini. He applies fertilizer to his crop twice during the growing season and notices that the second layer of fertilizer increases his crop, but not as much as the first layer. What economic concept best explains this observation?