A biologist wants to know the width of a river in order to properly set instruments for studying the pollutants in the water. From point A w

Thanks Alan,

Here is a pic

tan(θ) = width/70 so 

$${\mathtt{width}} = {\mathtt{70}}{\mathtt{\,\times\,}}\underset{\,\,\,\,^{\textcolor[rgb]{0.66,0.66,0.66}{360^\circ}}}{{tan}}{\left({\mathtt{54}}^\circ\right)} \Rightarrow {\mathtt{width}} = {\mathtt{96.346\: \!734\: \!432\: \!97}}$$

or width = 96 ft to the nearest foot.

(I've assumed the angle, θ, is between the line of sight to C and the line AB)

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Thanks Melody, the picture makes it much clearer.

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Thanks Alan, 

I had started the pic before you posted I just kept getting side tracted :)