Exercise 4 Page 348

Let's consider the given diagram. For the following explanation to be easier, we will name the vertices of the triangles.

As we can see, $\angle 9$ is an exterior angle to $△MLN.$ Because $\angle 6$ and $\angle 7$ do not share a vertex or corner of the triangle with $\angle 9,$ these are the corresponding remote angles. Let's now recall the Exterior Angle Inequality Theorem.

By this theorem, we can conclude that the measure of $\angle 9$ is greater than the measures of $\angle 6$ and $\angle 7.$ Moreover, $\angle 9$ is exterior angle to $△MLK.$ Because angles $\angle 1$ and $\angle 2$ also do not share a vertex or corner of the triangle with $\angle 9,$ these are the corresponding remote angles, whose measure less than $m\angle 9.$