The ribbon is 13 centimeters longer than the string. You would subtract the string's length from the ribbon's to get the difference. If your teacher wanted a decimal or percentage, you would set this up as a fraction. 24/11. This equals about 2.18 in decimal form. If this is needed as a percent, you take the decimal approximation and multiply it by 100 (percent=out of 100). The ribbon is 218% longer than the string.