Question

how to solve the area of the box as a product and sum

Answer 1

From the box we know that the area as a product is given by:

$3x(6x^2-x+9)$

And the result as a sum is given by:

$18x^3-3x^2+27x$

Then:

$3x(6x^2-x+9)=18x^3-3x^2+27x$