Firstly, I don't get your stated measurments of 10 x 10 x 3.5 .... The 3.5 is obviously the vertical dimension in the plane of the computer screen.
But the 10 x 10 ??
Perhaps the piece is 10" thick in the direction OUT of the screen (or supporting table).
But your tape measure in the pic seems to indicate more like 20" horizontal dimension, left to right. . Please clarify.
I'll assume your pictured piece is 10" thick in the direction out of the screen, with a pretty flat bottom perpendicular to the screen.
I would lay the flat bottom on your saw table and cut slabs of the exact shape shown in your pic, and with a thickness of about 7/8".
You should get about 10/0.875 = 11 such slabs after 10 such cuts ( saw blade kerf of about 0.04" ?? )
I do not like cross-cut grain for pens, so I would recommend cutting parallel to the long bottom (straight) edge after you have "slabbed" it.
That will get you 7 - 10 standard size blanks from each slab -- up to 4 or so with fairly straight grain and the rest with angled grain.
A total of close to 100 pen blanks ???
Of course, you may have something totally different in mind and not such a large number of pen blanks.
Maybe one oval-shaped bowl about 20 x 10 top opening with a depth of about 3 " ????
Should be able to rough that out with your saw.
But don't ask me how to turn such a bowl ? ... LOL !!