Answer:
<ECF = 45 degrees
Step-by-step explanation:
If ABCD is a square, then the diagonal AC divides angle <C and angle <A in two equal parts. Angles A and C are also 90 degrees each due to the act that the figure is a square. Therefore their bisection would render 90/2 = 45 degrees.
Notice as well that angle <ECF is opposite by the vertex to one of these 45 degree angles, and then it must measure the same amount (45 degrees).
So, <ECF = 45 degrees
