1 equation in 1 unknown
You are all making this much too complicated. Here is the equation where H is half the length of the bridge:
H / (H + 200) = (H - 3) / (200 - H + 3)
Each side is the ratio of the distance Charlie traveled to the distance the car traveled in the same amount of time. These are equal since the ratio of their speeds are equal. This gives the quadratic equation:
H^2 - 3H - 300 = 0
H = [ 3 + sqrt(9 + 1200) ] / 2
Length of bridge = 2H =~ 37.8 yards.
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