Darius's bag contains 3 times as many marbles as Tommy's bag. If Darius gives 3 marbles to Tommy, the two boys will have the same number of marbles. What is the total number of marbles?
Let the number of marbles Tommy has = N
Then Darius has 3N
And we have that
3N - 3 = N + 3
3N - N = 3 + 3
2N = 6
N = 6/2 = 3
So....the toal number of marbles = N + 3N = 3 + 3*3 = 12
+111 
