We are taking combination's with Joe, namely when the Joe stand the first, second, third and forth
then, if the Joe is the first, there 4! combination and take into account that Frankie can stand in the line 2nd, 3rd, 4th and 5th and 6th - all together 5 - therefore 4!*5
then if Joe is the second, Frankie can be 3rd, 4th and 5th and 6th - 4!*4
and so on, till Joe is the fifth, then frankie can be only the 6th and and the remaining 4 people can vary in the line totaling 4!
so 4!*5 + 4!*4 + ... + 4!*1 = 360