now, let's notice those tickmarks on the sides.
the ones at the bottom, those two sides are equal.
the ones at the top-right, those two sides are also equal.
what does all that mean?
it means that, the segment in the triangle, the 2x-3 segment is really the midsegment of the triangle, and therefore, also parallel to the base of 18, and also therefore is half of that length.
![\bf \textit{midsegment of a triangle}\\\\ m = \cfrac{b}{2}~~ \begin{cases} b=parallel~side\\ \qquad or~base\\[-0.5em] \hrulefill\\ m=2x-3\\ b=18 \end{cases}\implies 2x-3=\cfrac{18}{2}\implies 2x-3=9 \\\\\\ 2x=12\implies x=\cfrac{12}{2}\implies x=6](https://tex.z-dn.net/?f=%5Cbf%20%5Ctextit%7Bmidsegment%20of%20a%20triangle%7D%5C%5C%5C%5C%20m%20%3D%20%5Ccfrac%7Bb%7D%7B2%7D~~%20%5Cbegin%7Bcases%7D%20b%3Dparallel~side%5C%5C%20%5Cqquad%20or~base%5C%5C%5B-0.5em%5D%20%5Chrulefill%5C%5C%20m%3D2x-3%5C%5C%20b%3D18%20%5Cend%7Bcases%7D%5Cimplies%202x-3%3D%5Ccfrac%7B18%7D%7B2%7D%5Cimplies%202x-3%3D9%20%5C%5C%5C%5C%5C%5C%202x%3D12%5Cimplies%20x%3D%5Ccfrac%7B12%7D%7B2%7D%5Cimplies%20x%3D6)