Given
The area of the rectangle is represented as,

And, the length is represented as,

To find the breadth of the rectangle.
Now,
The area of the rectangle is given by,

Then,

Substitute the values of A and l in the above equation.
Then,

Since the common terrm in 14x^3-35x^2+42x is 7x.
Then,

Hence, the breadth of the rectangle is 2x^2-5x+6.