Since 5.7 calories are burned in one minute, we have that:
[tex]\frac{240}{5.7}=42.10526\ldots\approx42[/tex]
Then, if a person walks for 42 minutes, then they would burn exactly 239.4 calories.
So, a 150-pound person must walk for at least 43 minutes in order to use at least 240 calories (The answer is actually 42.105... but if we round down it to 42, that person would burn less than 240 calories. That's why it is better to round up).
