Assuming the sequence goes on like this 11,-33,99,-297,891,...,
its general formula is

So, the 9th term is
If you use the formula V=bh you can find the volume of a tranangular prism.
To find the area of the triangle you have to use the formula A=1/2bh
A=1/2(14)(20)=140ft2= Base of the triangle
V=bh V=140x30
V=4200ft2
Volume of cuboid=lenght*breadth*height
=3ft*3ft*5ft
=45ft^3