Here, You need to apply "Proportionality Theorem" According to this theorem, the ratio of components of a leg would be equal to the ratio of corresponding components of another leg.
In mathematical form, AB/BD = AC/CD
Substitute their values, 36/24 = x/18 2/3 = x/18 x = 18*3 / 2 x = 54 / 2 x = 27
