(Repost) (Please help) The area of a circle is decreasing at a constant rate of 393 square feet per minute. At the instant when the area of the circle is 64π ft^2, what is the rate of change of the radius? Round your answer to three decimal places. This is about related rates (calculus)

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Answer   (1) u.s.coast guard                (2)president major disaster declaration                (3) 72 hours;                 (4) u.s coast guard auxiliary;

Iam pretty sure it is c.

You need to figure out at which x-value does the graph has a tangent line slope of -1.remember, the derivative is the slope of the tangent line. so find the derivative function and set it to equal -1 to find the x-value that will have a tangent line slope of 0.differentiate with the chain rule.    set the derivative to equal -1 and solve for x.      take log base 10 of both sides. also recall that  .    so the x-coord of the point of tangency is .the y-coordinate of this point of tangency can be calculated using the original function:     using point-slope form, the equation of the tangent line is      the x-intercept of this tangent line is when the graph is at y=0.    this rounds off to  .choice c.