I'd do 9x4=36 because the 9 is from your money and the 4 is from your books. Now since you want to find out how much 4 books cost you just multiply that by 9
23.3 is your answer. Zyour welcome
angle a and angle e are obtuse angles
First we need to find the missing side, use

So the missing leg = the sqrt of the hypotenuse squared minus the other leg squared.
Let's substitute the numbers,

Solve for the squares,

Subtract,

Solve for the root,

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So our missing length is 8.
To find the perimeter of the triangle, simply add all the sides....
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Answer : 24
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I hope that helps you out!!
Any more questions, please feel free to ask me and I will gladly help you out!!
~Zoey