Since PQ and BC are parallel, we have the following:
That is to say, triangles APQ and ABC are similar. Since they are similar, their sides are proportinal. We can then see this relation in the following equation:
![(12+6)/(6)=(18+x)/(x)](https://img.qammunity.org/2023/formulas/mathematics/college/u9d8owbm0t4y0377nx75kh5cl3zsj9gyg2.png)
Where x is the lenght of AQ. We know rearrange the equation
![(18)/(6)=(18+x)/(x)](https://img.qammunity.org/2023/formulas/mathematics/college/3vcfb1d5stned4ongaifgxjer3bvo2u6ks.png)
![3=(18+x)/(x)](https://img.qammunity.org/2023/formulas/mathematics/college/76r0i0r1o2sn5gs6qm52qd7k1vx36kpnhn.png)
![3x=18+x](https://img.qammunity.org/2023/formulas/mathematics/college/hze6e1degmnzgrd0vi8buva1wt46sdq7lo.png)
![2x=18](https://img.qammunity.org/2023/formulas/mathematics/college/mdnkgetb7aw2nvdqncgafge4rbn7ov4lpw.png)
![x=9](https://img.qammunity.org/2023/formulas/mathematics/high-school/cmoob0b43q6h3m27uzhcp4tu0db7ka7bi8.png)
And so, the lenght of AQ is 9