where can I find the volume and cross section of this shape?

The first step is to subject the solid into two parts. We have
cuboid at the base and triangular prism at the top. Thus,
Volume = volume of cuboid + volume of triangular prism
The formula for calculating the volume of a cuboid is expressed as
V = length x width x height
From the diagram,
width = 9
height = 8
length = 12
Thus,
V = 12 x 9 x 8 = 864 cm^3
The formula for calculating the volume of a triangular base prism is expressed as
V = base area x height
base area = area of triangle = 1/2 x base x height
For the triangle,
base = 9
height = 15 - 8 = 7
Area of triangle = 1/2 x 9 x 7 = 31.5
Height of prism = 12
Volume of prism = 31.5 x 12 = 378 cm^2
Volume of shape = 864 + 378 = 1242 cm^3