Two sides ^@AB^@ and ^@BC,^@ and the median ^@AD^@ of ^@ \triangle ABC^@ are correspondingly equal to the two sides ^@PQ^@ and ^@QR,^@ and the median ^@PM^@ of ^@\triangle PQR.^@ If ^@AB = 11 \space cm, AD = 3 \space cm,^@ and ^@AC = 6 \space cm,^@ then the length of ^@ PR^@ is: