Help with Statics: Failing to See Force Fbc's Angle

[greekniko]

I'm sort of self-teaching statics. Failing to see why when they sum moments around A, the force Fbc is coming in at an angle (and hence being multiplied by the 5/13). Can someone please clarify?

 

[Simon Bridge]

Welcome to PF;
The question asks to calculate the moments etc "at a section passing through point E".