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A couple of other ways to approach . . .

\(l_1\) and \(l_2\) are cut by a transversal

Alternate interior angles are congruent.
Lower right angle = \(40°\)
Other angle of lower triangle, given = \(30°\)

1) \(x\) = exterior angle
Exterior angle \(x\) = sum of opposite interior angles of lower triangle
Exterior angle \(x\) \(= (30° + 40°) =\) \(70°\)

OR

2) Straight line: Third angle of lower ∆ + \(x = 180°\)
Interior angles of a triangle sum to 180°
Lower ∆'s third angle = \(110°\)
(\((180° - 30° - 40°) = 110°\) = third angle))

Third angle lies on a straight line with \(x\)
\(110° + x° = 180°\)
\(x = 70°\)


Answer A
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