This is in Differential Calculus. This is only multiple choice. Provide necessary solution. In case the answer is not in the choices, write the correct answer. Thank you and Godbless.

6. Sand is poured into a level horizontal surface at the rate of 15 ft /min. The sand pile forms a right circular cone whose altitude is always equal to its base diameter. How fast is its altitude increasing when the pile is 5 ft high? A) 2.12 ft/min C) 1.88 ft/min B) 1.22 ft/min D) 1.55 ft/min him d