A few key tips:

You should use NPV when:

• They say we should calculate out into perpituity (i.e. forever)
• They provide you with a discount rate, cost of equity/capital, etc.
• There is a set growth rate (into perpituity)
• They want a calculation into the next year or two
• As a default (i.e. always say "I could do NPV if needeD"

You should not use NPV when:

• You have offered and they say no
• For any calculations that are >= 3 years or < inifinity

The reason? They don't expect you to do the crazy math that NPV requires further than to the power of 2/3.

In this case, the answer is provided here: "Total recurring profits = High season profits + Low season profits = 180 * x * 125 * ( $600 - $100) + 180 * 60% * 125 * ( $400 - $100) - $2.17M "

(edited)