refering to Statics and mechanics of materials RC Hibbeler 3

(refering to Statics and mechanics of materials R.C. Hibbeler 3rd edition Si chapter 4 problem 23p Step 5 in worked solutions) I am unsure of why the moment created by Fa is multiplied by 2sin(45) instead of (perpendicular distance from B to A)sin(45)

The question asks for the support reactions of roller A and the smooth collar B on the rod (The collar is fixed to the rod AB but is allowed to slide along rod CD.)

Solution

moment= force*perpendicular distance

sin 45= (perpendicular distance/ hypotenus )= (perpendicular distance/2)

perpendicular distance= 2sin45(this is how it comes)