  The 4-qubit unextendible product basis (UPB) has been recently studied by
[Johnston, J. Phys. A: Math. Theor. 47 (2014) 424034]. From this result we show
that there is only one UPB of size $6$ and six UPBs of size $9$ in
$\cH=\bbC^2\ox\bbC^2\ox\bbC^4$, three UPBs of size $9$ in
$\cK=\bbC^4\ox\bbC^4$, and no UPB of size $7$ in $\cH$ and $\cK$. Furthermore
we construct a 4-qubit positive-partial-transpose (PPT) entangled state $\r$ of
rank seven, and show that it is also a PPT entangled state in $\cH$ and $\cK$,
respectively. We analytically derive the geometric measure of entanglement of a
special $\r$.
