If you take random point and across would be like this

0( imagine "0" as a dot/point as it more visible

(0

0)

this would be the across of the point

and the angle of depression is a downward slope and it says 30 degrees

so join those two points and mark the internal angle as 30 degrees now the first point as 4 degrees .

now there are saying that the bridge is of a height 4m so draw a straight line from point B(second point).now join all the points.(note: it forms a triangle im unable to draw over here think carefully and observe properly).if u dont know this property now you would be learning one.the sum of interior angles of a triangle is 180 degrees.

so it 180-30-45=105 degrees.and the width is = area of a triangle =1/2 multiplied by base multiplied by width(bredth)

180= 1/2 multiplied by 3 mutiplied bywidth(note: in this context 180 would be the area as the length and other figures are unknown).

so its 360 divided by 3

=120m which is the width

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