The formula for the area of a rectangle is:
Area = length x width
We know the width is 3.9 cm and the area is 25.311 cm². Let's plug these values into the formula and solve for the length:
25.311 = length x 3.9
length = 25.311/3.9
length ≈ 6.49 cm
Therefore, the length of the rectangle is approximately 6.49 cm, which corresponds to option C.