A hotel has 72 rooms.

Rooms are usually $90 per night.

But if the owner raises the price to $95 per room per night, he finds that there will be 2 rooms fewer than usual($90 a room per night) hired.

I am not sure whether for EVERY $95 dollar room, 2 rooms are left vacant, or are 2 rooms of the 72 rooms in total left vacant.

I think our teacher said that the Income formula that we have to calculate is:

Income = 108x - [or maybe +] (2x^2)/5

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1. Find the formula to calculate the income

2. Calculate the maximum Income

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Could someone please explain calculus word problems like this to me in detail?

Thank You! :)