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.