Help math review in physics?

Question

Why is this AP Physics? anyway, i kno its pathetic for a physics student to be asking this, but i forget everything from geometry. please help. automatic best answer to correct answer

A student wants to determine the distance of a small island from the lakeshore, as shown in figure. He first draws a 50-m line parallel to the shore. Then, he goesto the ends of the line and measures the angels of the lines of sight from the island relative to the line he has drawn. The angles are 30 degrees and 40 degrees, how far is te island from the shore?

Answer 1

Draw a perpendicular from island to 50m line on shore.Call it y

50m line on shore is divided up x on one side, 50-x on the other

you have 2 triangles

triangle 1)  tan30 = y/x

triangle 2)  tan 40 = y/(50-x)

So y=(x)(tan30)

and y=(50-x)(tan40)

(x)(tan30)=(50-x)(tan40)

x=29.61

y=(x)tan30

y=29.61(tan30)

y=17.1

Why is this AP Physics?  Analgous to calculating distances to stars using parallax----distance between opposite points on earth's orbit is like the line in the sand.  You can measure the angle to the star and calculate its distance using the same method.  

There may be an easier way to solve your problem but this works for me