Answer:
7 units 
Step-by-step explanation:
Please refer to the image attached with this answer.
Our initial line was CD  joining points (-1,2) and (6,2). 
It is now pulled down by 4 units , to new points 
(-1,-2) and (6,-2)
Now we again shift this line by 2 units to the left. The new coordinates thus would be C'(-3,-2) and D'(4,-2)
Hence the distance C'D' = 4-(-3) = 4+3 = 7 UNITS
Hence the length of the line will be 7 units.  
It is observed that the length of the line segment remains the same as it was of the original line. as the translation is uniform.