Answer: Tropic of Cancer
The Tropic of Cancer is one of the parallels (imaginary line around the Earth parallel to the equator) located in the northern hemisphere. It is called "Cancer" because a long time ago, when the summer solstice occurred in the northern hemisphere (on June 20th or 21st), the Sun was in the constellation Cancer (the crab). However, it is currently in the Taurus constellation.
On the other hand, the Tropic of Capricorn is a parallel to the southern hemisphere. It is called "Capricorn" because in the antiquity, when the summer solstice occurred in the southern hemisphere (on December 20th or 21st), the Sun was in the constellation of Capricorn, but now it occurs in the constellation of Sagittarius; nevertheless this tropic continues with this name by tradition.
Then, based on this explanation, the imaginary line that is farther north is the Tropic of Cancer.