Prove that the measure of the angle... 
How can I prove that the measure of angle $EBC$ is $60$?
Thank you!

HINT
The two triangles with the $15^{\circ}$ angles are both isosceles. If you know that $ABCD$ is a square then they are, in fact, congruent triangles. That allows you to start putting little dashes on all of the sides of equal length. Then when two sides of a triangle with unknown angles have the same lengths for two of their sides you know that it's isosceles and know that two of its angles are equal.
Try it. You get to the answer pretty quickly.
