In the given figure, the tunnel is in the shape of a cylinder.
The diameter of the tunnel, D=4 ft
Hence, the radius of the tunnel is,

The height of the cubical block, a=6 ft.
The height of the tunnel is the same as the height of the cubical block.
Hence, the height of the tunnel, h=a=6 ft.
Now, the volume of the tunnel in the shape of a cylinder can be calculated as,

Therefore, the volume of the tunnel created inside the block is 75.4 sq.ft.