Final answer:
The length of the line after the enlargement is 63 cm.
Step-by-step explanation:
To find the length of the line after the enlargement, we need to multiply the scale factor by the original length. In this case, the scale factor is 7 and the original length is 9 cm.
So, the length of the line after the enlargement is 7 * 9 = 63 cm.