The length of a rectangular box is ( x + 9y) and the area is x² + 12xy + 27y². Find the breadth.

Area of a rectangle = length x breadth, hence breadth = area / length.
breadth = x² + 12xy + 27y²
( x + 9y )
= x² + 9xy + 3xy + 27y²
( x + 9y )
= x ( x + 9y ) + 3y (x + 9y)
( x + 9y )
breadth = x + 3y