Two massless bags contain identical bricks, each brick having a mass MM$.$ Initially, each bag contains four bricks, and the bags mutually exert a gravitational attraction F$1$F$1$ on each other. You now take three bricks from one bag and add them to the other bag, causing the bags to attract each other with a force F$2$F$2.$ What is the closest expression for F$2$F$2$ in terms of F$1$F$1?$

F$2=716$F$1$F$2=716$F$1$F$2=3$F$1$F$2=3$F$1$F$2=4$F$1$F$2=4$F$1$F$2=$F$1$F$2=$F$1$ because neither the total mass nor the distance between the bags has changed.