7. A stone is dropped into a still pond. Concentric circular ripples spread out, and the radius of the disturbed region increases at the rate of 16 cm/sec At what rate does the area of the
disturbed region increase when its radius is 4 cm?

answer:

your answer is: c. 196 7/8 in^3.

or

step-by-step explanation:

we need to solve for 'x' the following equation:  

we have that:

⇒

⇒ ⇒

factorizing, we get that:

  ⇒

then, the solutions are: or

nothing extraneous has been found!

the answer is 8/21

hope this