A wall is 4 m high and 40 cm wide. It contains two windows of din 2.5 m X 1 m and a gate way of dimensions 2 m x 3 m. If 2450 cubical slab
length 20 cm are required to construct the wall, find the length of the wall​

geometry: triangles

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call the larger triangle abc

then the smaller triangle cde is similar to abc (all angles are equal, aaa).  

ab is the side that is 36, and we wish to find de, the side corresponding to ab

area_cde = area_abc - area_cde --> area_abc / area_cde = 2

let x=length of de

ratio of areas = (ratio of sides)^2

+2+=+%2836%2fx%29%5e2+

+2+=+1296%2fx%5e2+

++x%5e2+=+1296%2f2+=+648+

25.45584