Question 1089952
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Second plank: x meters long.

First plank: 3x - 16 meters long.

Both together are x + (3x-16) = 4x - 16.


Your equation is 

4x - 16 = 8.


Your solution is 

4x = 8 + 16 = 24  ====>  x = 6.


<U>Answer</U>.  Second plank is 3 m.  First plank is 3x-16 = 3*6 - 16 = 2m.
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Solved.