Explanation:
The width is 6 cm, but the other dimension is unknown, that will be ''X''.
So, the area of the rectangle would be according to the expression:
[tex]A = x . 6 (cm)[/tex]
They want us to find a range of lengths with an area minor than [tex]126 cm^{2}[/tex]
Therefore, this is an inequality problem, which expression will be:
[tex]x . 6 < 126\\x < \frac{126}{6}\\ Hence, x < 21\\[/tex]
Finally, the length's range that ensure an area less than 126, it's all length less than 21.