399.6 square meters
7•8/2=28
28•3=84
8•6.9/2=27.6
(12•8)•3=288
84+27.6+288=399.6
Using the t-distribution to build the 99% confidence interval, it is found that:
- The margin of error is of 3.64.
- The 99% confidence interval for the population mean is (19.36, 26.64).
<h3>What is a t-distribution confidence interval?</h3>
The confidence interval is:

In which:
is the sample mean.
- s is the standard deviation for the sample.
The critical value, using a t-distribution calculator, for a two-tailed 95% confidence interval, with 21 - 1 = 20 df, is t = 2.086.
The other parameters are given as follows:

The margin of error is given by:

Hence the bounds of the interval are:


The 99% confidence interval for the population mean is (19.36, 26.64).
More can be learned about the t-distribution at brainly.com/question/16162795
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We are asked in the problem to determine the value of x in the equation <span>4x² + 2x = 7 using completing the square method. in this case,
</span><span>4x² + 2x = 7
x2 + 0.5 = 1.75
(x + 0.25)^2 - 0.0625 = 1.75
</span>(x + 0.25)^2 = 1.8125
<span>x+0.25=1.3462
</span>x1 =1.0963
x2 =-1.5962
Mean is 64 and the mean absolute deviation is 12.5
We know:

and

These expressions have an
term in common. We can combine them if we can find forms of the expressions in terms of
:


Now, because
(by the reflexive property), we can write:

This is our answer, A.