Answer:
36.21 minutes
Explanation:
To determine how long a person must walk at a speed of 4 mph to use at least 210 calories, we need to divide the number of calories needed by the number of calories used per minute.
First, let's convert the weight of the person to kilograms by dividing it by 2.2: 150 pounds / 2.2 pounds/kilogram = 68.18 kilograms
Now, let's convert the speed of the person from mph to m/s by dividing it by 2.23694: 4 mph / 2.23694 mph/m/s = 1.78 m/s
Next, let's use the formula for the metabolic rate (R) of a person walking to calculate the number of calories used per minute: R = 0.0273 x M x V + 3.91, where M is the person's weight in kilograms and V is their speed in m/s.
Plugging in the values we have calculated above, we get: R = 0.0273 x 68.18 x 1.78 + 3.91 = 5.8 calories/minute
Finally, we can divide the number of calories needed (210 calories) by the number of calories used per minute (5.8 calories/minute) to find the number of minutes required: 210 calories / 5.8 calories/minute = 36.21 minutes
Therefore, a person walking at a speed of 4 mph must walk for approximately 36.21 minutes to use at least 210 calories.