Answer:
The length of the beam increasing is 9.64 ft/s.
Explanation:
Given that,
Height = 210 ft
Distance =290 ft
According to figure,
We need to calculate the angle
....(I)
Put the value of x in the equation


Now, 
On differentiate of equation (I)


Put the value in the equation



Hence, The length of the beam increasing is 9.64 ft/s.
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The answer is going to be B: elevation.
the answer your looking for is Optical instrument.
The dna is multiplied obviously