Answer: 
Step-by-step explanation:
Given
The tower is at a height of 
the angle of depression is 
Suppose the surfer is x ft away from the base of the tower

Therefore, the surfer is at a distance of 19.31 ft from the base of the tower.
It's not the difference of squares, rather it is the square of a difference. That leaves a perfect square trinomial, which narrows your selection to two choices. An expression with 2 terms is not a trinomial, so that further narrows your selection. The appropriate choice is
... (4xy -3z)² = 16x²y² -24xyz +9z², a perfect square trinomial
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The expression you have in your problem statement has no z term, so none of the choices is applicable to that one.