In this problem we have that
XY is parallel to QR
triangle PQR is similar to triangle PXY
\(PY=YR \\PX=XQ\)
so
by proportion
\(\frac{QR}{XY}= \frac{PR}{PY}\)
we have
\(XY=4\ units\)
\(PR=2PY\ units\)
substitutes
\(\frac{QR}{4}=\frac{2PY}{PY}\)
\(\frac{QR}{4}=2\)
\(QR=8\ units\)
therefore
the answer is
\(8\ units\)
