Sally bought a few marbles and divided it equally among four of her friends and her brother, George. While playing, George lost 2 marbles and has only 7 marbles at present. Find how many marbles Sally bought in all.

So if George lost 2 marbles, and he now has 7 ... then he originally had 9 marbles to begin with.

and if Sally bought the marbles and split them equally with 4 friends and her bro ... so she split them equally with 5 people ... and being she gave George 9, then she gave all the others 9 as well.

that means that she bought (9 * 5) = 45 marbles <==

Sally bought 45 marbles. She gave it to 5 people. And George had 9 marbles. So 9 times 5 is 45.