$\Delta ADC$ có $MQ\,\,||\,\,DC$
$\to \dfrac{MD}{MA}=\dfrac{QC}{QA}$ ( định lý Ta – let )
$\to QA=\dfrac{MA\,.\,QC}{MD}=\dfrac{10\,.\,35}{20}=17,5\,\,\left( cm \right)$
$\Delta ABC$ có $QN\,\,||\,\,AB$
$\to \dfrac{QA}{QC}=\dfrac{NB}{NC}$ ( định ly Ta – let )
$\to NC=\dfrac{QC\,.\,NB}{QA}=\dfrac{35\,.\,11}{17,5}=22\,\,\left( cm \right)$