You earn $9 per hour for 15 hours of work. You spend $20 of your earnings on gasoline. Three choices show ways to calculate how much money, m, is left after you buy gasoline. Which choice does NOT?
Money left = 15 hours • $9 per hour – $20
m = $9 per hour • 15 hours – $20
m = 15 hours • $9 per hour, or $20, whichever is greater
Subtracting $20 from 15 hours times $9 per hour

Question

You earn $9 per hour for 15 hours of work. You spend $20 of your earnings on gasoline. Three choices show ways to calculate how much money, m, is left after you buy gasoline. Which choice does NOT?
Money left = 15 hours • $9 per hour – $20
m = $9 per hour • 15 hours – $20
m = 15 hours • $9 per hour, or $20, whichever is greater
Subtracting $20 from 15 hours times $9 per hour

anonymous · Answer

Usually they don't let you pick whichever is greater.

compassionate · Answer

The first and second one are the exact same thing. 
The last one is the same operation as the first one, just backwards. 

You should not pick which one is greater. This is improper.