Answer :
In 139.4 [tex]\pi[/tex] [tex]ft^2[/tex]sec rapidly is area of enclosed by the ripple increasing at the end of 6.4 seconds.
What is area of circle?
For measuring the area occupied by a circular field or plot, use the area of a circle formula. The area formula will allow us to determine how much fabric is required to completely cover a circular table, for example. We can determine the boundary length, or the circle's circumference, using the area formula.
Here area of circle
=> A= π[tex]r^2[/tex]--------> 1
Differentiating 1 with respect to to time then
=> [tex]\frac{dA}{dt}= 2\pi r\frac{dr}{dt}[/tex]
If the radius is increasing at a constant rate 3.3ft/sec then after 6.4 seconds, radius is
=> 6.4*3.3=21.12 ft.
We know [tex]\frac{dr}{dt}= \frac{3.3ft}{sec}[/tex] and so ,
=> [tex]\frac{dA}{dt}[/tex] = 2*[tex]\pi[/tex]*21.12*3.3=139.4 [tex]\pi[/tex] [tex]ft^2[/tex]sec.
Hence In 139.4 [tex]\pi[/tex] [tex]ft^2[/tex]sec rapidly is area of enclosed by the ripple increasing at the end of 6.4 seconds.
To learn more about area of circle refer the below link
https://brainly.com/question/10645610
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