Here is the original problem and a valid rewording of each sentence:

"The area of a circular doggie puddle is growing at a rate of 12 cm²/s."

  translates to: "The rate of change of area = 12."

How fast is the radius growing at the instant when it equals 10 cm?

  translates to: "Find the rate of change of radius at the instant when the radius = 10 cm."