9514 1404 393
Answer:
51°
Step-by-step explanation:
The angles where the expressions are given are a linear pair, so total 180°.
(3x +15) +(10x +9) = 180
13x = 156 . . . . . . . . . . . . . . . subtract 24, collect terms
x = 156/13 = 12
Then the acute angle is ...
3x +15 = 3(12) +15 = 36 +15 = 51
The stairs make an angle of 51° with the basement floor.
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<em>Additional comment</em>
Building code requires the rise to be not more than 8 and the run not less than 9, so the maximum angle is about 41.6°. A 51° staircase would not meet code.
