Divide The Cake Into Equal Parts!

I have just baked a rectangular cake when my wife comes home and barbarically cuts out a piece for herself. The piece she cuts is rectangular, but it’s not in any convenient proportion to the rest of the cake, and its sides aren’t even parallel to the cake’s sides. 

 
I want to divide the remaining cake into two equal-sized halves with a single straight cut. How can I do it?



This is how it can be cut! 

Cutting The Cake Into Equal Parts!

What was the problem? 

Generally, a line drawn through the center of rectangle divides it into 2 equal parts.
Hence, a line drawn through the centers of both rectangles would divide each of them into 2 equal parts as shown below. (To get the center of each rectangle, all we need to do is draw diagonals of both).