We need to calculate how many inches we cut off. Knowing that, we subtract that amount to the total length of the rope and we have the length of what remain.
We cut 6 pieces of 18.5 inches long each. The total of inches that we cut off is 6*18.5 = 111 inches.
Now we subtract 111 inches to the original length of the rope:
129.25 - 111 = 18.25 inches
The rope is 18.25 inches long after we cut off the 6 pieces.
