



 
Hi Joanna, You use the terms horizontal and vertical so I am assuming the the angles $CDA$ and $DAB$ in my rough sketch are right angles. I drew the line $BE$ parallel to $DA$ and hence angle $CEB$ is a right angle and hence we can use Pythagoras Theorem on the triangle $CEB.$ thus \[BC^2 = CE^2 + EB^2 = (2560  1850)^2 + 1750^2 \;mm^2\] and hence \[BC = \sqrt{3566600} = 1888.54 \;\; mm\] Penny  


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