Question 1062790
Apothem=r cos (180/n), r=6 units
=6cos 180/10=6 cos 18=5.71 units, C.
1/2 the side is 6 sin 18=1.854 units
That makes the side 3.708 units, and the altitude is 5.71 units.
That product is 21.173 units.  The area is 1/2 of that, and there are 10 such triangles in a decagon, so multiply 21.173*5=105.86.  That rounds to 106 sq units or B.