The 270° CCW rotation is described by the transformation ...
(x, y) ⇒ (y, -x)
That is, the first row of the transformed coordinate matrix is the same as the second row of the input matrix. The second row of the output matrix is the opposite of the first row of the input matrix.
He is trying to find the volume of the big box. He does that by multiplying all the sides such as 10cm*8cm*12cm=960cm³. A 1 cm cube represents 1cm<span>³ in the big box. He will be able to fit 960 of the small cubes in the big box.</span>