4. As shown in the figure, $\angle 1$ equals 100 degrees, $\angle 2$ equals 60 degrees, $\angle 3$ equals 90 degrees. Please answer: $\angle 4$ equals $\qquad$ degrees.
Analysis: The sum of the exterior angles of any polygon equals $360^{\circ}$.
Therefore, $\angle 4=360^{\circ}-\angle 1-\angle 2-\angle 3=360^{\circ}-100^{\circ}-60^{\circ}-90^{\circ}=110^{\circ}$.