Split a rectangle

As
Pieter Torbijn fooled us with our last contest (he was right though) this
new contest came alive.

Start with a set of pentominoes :

Place a pentomino in each corner of a rectangle.

The length and width of the rectangle may at most be 16 units long.

Then place the other pentominoes in such a way, that every pentomino borders
at least one other pentomino by the length of at least one unit.

All pentominoes must fit completely inside the rectangle; also each one of
them must cover just 5 unit squares on the grid.

There must be just 2 empty areas of equal size.

Your challenge is to maximise these two areas.

In
our example, both areas contain 66 unit squares.

This Excel file
will make searching
for a solution a bit easier.

To download it click with the right mouse button and choose ‘Save target as
...’ to save this Excel file on your hard disk or diskette.

An help in
searching for solutions is the program “FlatPoly2”. You can download it from
the homepage of Aad van de Wetering, Driebruggen.