The picture isn't quite clear, so i have include a clearer one in the attachment below.
We need to determine the altitude of segment BD. From taking a look at the picture I can conclude that these triangle( s ) formed through the camera's positioning are proportional to one another, but here is the evidence -
( By Vertical Angle's Theorem, [tex]m<FDE = m<ADC[/tex]
( By Alternate Interior Angle's Theorem, [tex]m< EFD = m<ACD[/tex]
( Respectively by Alternate Interior Angle's Theorem, [tex]m< FED = m<CAD[/tex]
Therefore we can conclude that these triangle are similar to one another, and hence we can create a proportionality as such ( with the lengths ) -
[tex]20m / 125m = 10m / x[/tex]
And this " x " is the length of segment BD, which we want to determine -
[tex]20 / 125 = 10 / x - ( Cross Multiply ),\\20x = 125( 10 ),\\20x = 1250,\\\\x = 1250 / 20,\\x = 62.5 m[/tex]
The altitude with which the camera should be flown is 62.5 meters.
Hope that helps!