OKay well first you have multiply, so 4 x 9 = 36. Now you have to try to find how many songs will fit into 7 groups. So 5 is the maximum number for each group. cause 5 x 7 equals 35. But if you try to do 6, 6 x 7 which equals 42 which is too much, so 5 in each group. Now we have to try to find how many are left over, so we subtract, 36-35 equals 1. So you have one song over.
Hope I Helped!!! :D