Question 945793
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You need to make a habit of using brackets. You were right in recognizing that the length was 3x. Since 3x=a, so when you find a^2, you have to square the whole of 3x. However you thought it was {{{3(x)^2}}}, when it was actually {{{(3x)^2}}}. So if you had used brackets you probably would have gotten the right answer.