A^2 + B^2 = C^2
6^2 + B^2 = 7^2
36 + B^2 = 49
B^2 = 13
B = 3.61
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Answer: 
Step-by-step explanation:
Let be "x" the time in minutes a 150-pound person must walk at 4 mph to use at least 190 calories.
The amount of calories that a 150-pound person uses in 1 minute when walking at a speed of 4 mph is:

Therefore, knowing this, we can write the following proportion:

Finally, we must solve for "x" in order to find its value.
Multiplying both sides of the equation by 190, we get this result:

We want to find the value that makes

To find it we must look at the standard normal table, using the complementary cumulative table we find that

Then, using the z-score we can find the minimum score needed, remember that

Where
σ = standard deviation
μ = mean
And in our example, x = minimum score needed, therefore

Rounding to the nearest integer the minimum score needed is 568, if you get 568 you are at the top 20.1%.