Answer:
[tex]x \ = \ 10[/tex]
Step-by-step explanation:
Let point [tex]D[/tex] be the point where the straight line drawn from point [tex]A[/tex] meets the straight line [tex]BC[/tex], it is evident that [tex]\triangle ABD[/tex] and [tex]\triangle ACD[/tex] is similar given that both triangles share the same angle, [tex]\angle BAD \ = \ \angle DAC[/tex]. Hence, the ratio of the sides of each triangle is the same. Specifically,
[tex]\displaystyle{\frac{x+4}{8} \ = \ \frac{2x+1}{12}}[/tex].
Performing cross multiplication yields
[tex]12\left(x+4\right) \ = \ 8\left(2x+1\right) \\ \\ \rule{0.15cm}{0cm}12x+48 \ = \ 16x+8 \\ \\ \rule{1.1cm}{0cm} 4x \ = \ 40 \\ \\ \rule{1.3cm}{0cm} x \ = \ 10[/tex].
