JAMB 2014 · UTME · Q27

From the figure, what is the value of $p$ ?

Worked solution (try it first)

Vertically opposite angles are equal, so $q = 30^\circ$ .
The angle $(p + 2q)^\circ$ and the $30^\circ$ angle lie on a straight line, so $p + 2q + 30 = 180$ .
Put in $q = 30$ : $p + 60 + 30 = 180$ , so $p = 90^\circ$ , option B.