Step-by-step 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:

They want us to find a range of lengths with an area minor than

Therefore, this is an inequality problem, which expression will be:

Finally, the length's range that ensure an area less than 126, it's all length less than 21.