How do you find the volume of an l-block

To work this out, you need to picture the L as two different cuboids.

The " I "part of the L and the " - " part of the L .

You get the dimensions of "height, width, length"  of the " I " part, multiply them together. Save this number

Then you do the same for the " - " part of the L. Save this number

Add the two numbers you saved.