Free Fall Differential Equations Problem - I am stuck

Question:

An Object of mass 5.00 kg is given an initial downward velocity of 74.5 m/sec and then allowed to fall under the influence of gravity. Assume the force due to air resistance (in N) on this object is twice its speed. If it hits the ground in exactly 10 seconds, how many meters above the ground was the object when it was released?

The answer should be 368.

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The part I am stuck in this problem is what will be the drag co-efficient? It says "Assume the force due to air resistance (in N) on this object is twice its speed." - This is the part I DO NOT understand at all!!! :o

Please help! :) Thanks