We used trial and improvement to solve this question.
For example,78 is a multiple of 3 so we tried that number.
78. 7 squared is 49. 8 squared is 64. 64 - 49 =15 And add the numbers(7+8)is 15.
15 is a factor of 15.
We tried another one. 48. 4 squared is 16. 8 squared is 64. 64 - 16 = 48 Add the digits of the original number(4+8)which is 12. 12 is a factor of 48.
For the 5 Multiples one,we used 95 as an example. 9 squared is 81 and 5 squared is 25. 81 - 25 =56
Add the digits of the original number(9+5)which is 14. 14 is a factor of 56.
To prove it we used another number. 65. 6 squared is 36. 5 squared is 25. 36 - 25 = 11 Add the digits of the original number equals to 11. 11 is a factor of 11.
So its safe to say that in algebraic form is
MN. M squared. N squared. The squared numbers subtract each other equals a multiple of (M + N)