Final answer:
The expression representing the cost to buy and maintain one humidifier for n weeks is 640 + 40n dollars, with 640 being the purchase cost and 40n being the total maintenance cost over n weeks.
Step-by-step explanation:
The question requires us to write an expression that represents the cost to buy and maintain one humidifier for n weeks. Given the total cost function 640 + 40n, we can interpret the value 640 as a one-time purchase cost of the humidifier and the 40n as the maintenance cost that accumulates each week for n weeks.
Therefore, the expression that represents the cost to buy and maintain one hum2idifier for n weeks is simply the same as the given total cost function: 640 + 40n dollars. The term 640 is the initial cost for purchasing the humidifier, and 40n represents the total maintenance cost for n weeks.