We are asked to determine the radius of a cone given its volume and its height. To do that we will use the following formula for the volume of a cone:

Now, we solve for the radius "r". First, we multiply both sides by 3:

Now, we divide both sides by pi and the height:

Now, we take the square root to both sides:

Now, we convert the height from feet to yards using the following conversion factor:

Multiplying by the conversion factor we get that the height is 1 yd:
Now, we substitute the values:

Solving the operations:

Therefore, the radius is 21 yd.