1- Put a green sphere at the end of the bottom string.
2- Put a green sphere at the end of the middle string.
3- Switch green color to white color.
4- Switch white color to red color.
5- Collapse the bottom string using a red sphere.
6- Add a red sphere to the middle of the middle string.
7- Collapse that string with a red sphere.
8- Collapse the upper string with a red sphere.
9- Collapse the resulting string on the left using a red sphere