Answer:
x = 40 1/2
Explanation:
The hash marks tell you the triangles are similar and the smaller one is 1/2 the size of the larger one. Then x is half the length of the corresponding segment marked 81.
x = 81/2
x = 40 1/2
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You may have to write it as 81/2 or as 40.5. Sometimes the answer needs to be in a particular form.