Nine eggs weigh 9 * 1/20 = 9/20kg.
After a rope is cut180m, the remaining rope is three times as long as it was cut. How long is this rope?
The rest accounts for the whole length: 3/( 1+3)=3/4.
The original length is: 180/( 1-3/4) = 720m.
Or: original length = 180+3* 180=720.