So L 1 is parallel to L2 (internal dislocation angles are equal and two straight lines are parallel).
So ∠ 1=∠4 (two straight lines are parallel and have the same angle).
Because < 5+< 6 =180.
So L2 is parallel to L3 (complementary to the inside corner, two straight lines are parallel).
So ∠4=∠6 (two straight lines are parallel and have the same angle.
So < 1 = < 6.
Because ∠ 6+∠ 7 = 180.
So ∠ 7 = 125 39 minutes and 44 seconds.