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I am getting approximalte half what the answer should be (Related Rates Problem)

I am having trouble with this question but I believe it's a small mistake because I get approximately half of what the answer should be. I attached my work.

__Question:__ "A ladder 10 ft long leans against a vertical wall. If the bottom of the ladder slides away from the base of the wall at a speed of 2 ft/s, how fast is the angle between the ladder and the wall changing when the bottom of the ladder is 6ft from the base of the wall?

__Answer:__ 1/4 rad/s

Any help would be greatly appreciated!

Thanks in advance!