Answer:
m<5 == m<1 since alternate interior angles are same value
m<3 == m<6 since alternate interior angles are same value
m<6 + m<5 + m<2 = m<1 + m<2 + m<3 = 180
Explanation:
The use of alternate interior angles definition allows for you to make this completion. You can use this since you have a line intersecting a point on two parallel lines. From here, you know that the measures of the angles are the same as the measure of the line, thus you have proven the internal sum of angles to be 180 degrees.