Answer: 34.8 degrees (approximate)
The diagram is shown below.
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Work Shown:
tan(angle) = opposite/adjacent
tan(theta) = 12.5/18
theta = arctan(12.5/18)
theta = 34.7778313663639
theta = 34.8 degrees
Round this value however your teacher instructs. I decided to round to one decimal place because the 12.5 is to one decimal place. Make sure your calculator is in degree mode.
The notation arctan refers to arctangent. It is the same as inverse tangent, and it is often shown as
on many calculators.