The area of a rectangle is expressed as (12m + 18) square feet. If the width of the rectangle is 6 feet, choose an expression to represent the length of the rectangle. (m + 1) feet (2m + 3) feet 6(12m + 18) feet (6m + 12) feet

Length = Area / Width

Length = $(12m + 18) / 6$

To simplify, divide each term in the numerator by the denominator:
Length = $\frac{12m}{6} + \frac{18}{6}$
Length = $2m + 3$

Therefore, the expression representing the length of the rectangle is $(2m + 3)$ feet.

The final answer is $\boxed{(2m + 3)\ \text{feet}}$.