Pls help I will mark BRAINLIST
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The empirical rule you're referring to is the 68-95-99.7 rule, which asserts that for a normal (bell-shaped) distribution, approximately 68% of the distribution lies within 1 standard deviation of the mean; 95% lies within 2 standard deviations of the mean; and 99.7% lies within 3 standard deviations of the mean.
Let be the random variable denoting vehicle speeds along this highway. We want to find
. To use the rule, we need to rephrase this probability in terms of the mean and standard deviation.
Notice that , and
. In other words, 61 and 79 both lie exactly 3 standard deviations away from the mean, so
.
The subtraction sign in front of the second set of parenthesis changes the signs on the terms inside those parenthesis. So this could be rewritten as 
. None of the exponents on the x are the same, so we will just express it in terms of descending powers of x. 
. This is also the same as 
if you don't like to start with a negative. Either one is correct.