Answer: the length of the white rope is 77 inches.
Step-by-step explanation: The yellow rope is 18 inches shorter than twice the length of the white rope. If Y is the length of the yellow, and W the length of the white one, this can be expressed as 2*W - Y = 18 inches.
now we know that Y = 10 +1/2 feet = 10.5 feet.
and 1 feet = 12 inches, then Y= 10.5*12 = 126 inches.
putting it in the equation that we found earlier, we got 2*W - 126 = 18
then: 2*W = 126 + 18 = 144 inches
W = 144/2 = 77 inches.