Let S be the set consisting of the number 258131 together wi

Let S be the set consisting of the number 258131 together with all other different numbers formed by rearanging its digits. FInd the sum of the element S.

Could you show me why do we fix the last digit as the number of possible combinations and how do we know it is 60.

If the total number of digits = 6 and number of repetition = 2 as there are two 1 So total number of possible elements = 6P6/ 2 = 360 (answer)