Asked by sidath kularatne :)

b) Using the digits 1, 2, 3, 4.
5 and 6 once, arrange them
to make an addition
calculation with a total of
660.
__ __ __+ __ __ __ = 660
Answered by oobleck
4+6 = 10 - that provides the final zero, and carries the 1
so, now you want two numbers which add to 65, using the digits 1,2,3,5
That should not be too hard