Find possible expressions for the length and breadth of each of the following rectangles whose areas are given by the following expressions in square units.
(A) $25a^2 - 30ab + 9b^2$
(B) $36s^2 - 49t^2$

(A) $$\text{Area} = 25a^{2} - 30ab + 9b^{2}$$
$$= (5a)^{2} - 2(5a)(3b) + (3b)^{2}$$
$$= (5a - 3b)^{2}$$
$$\text{Length} = \text{breadth} = (5a - 3b) \text{ units}$$

(B) $\text{Area} = 36s^2 - 49t^2$
$= (6s)^2 - (7t)^2$
$= (6s + 7t)(6s - 7t)$
$\text{Length} = (6s + 7t), \text{Breadth} = (6s - 7t)$