find the largest 7-digit number which satisfy these 2 properties 0-9

- no two digits in the number are the same

- each of the number’s digits divides into the number exactly

a. FIND 3 digits which can't be in this number and EXPLAIN why we cannot use them

b. what is the highest 7 digit number you can make? EXPLAIN why it is the largest 7 digit you can make

c. what is the SMALLEST number you can make which ALSO satisfy the properties

any answers, hints, help discussion etc greatly appreciated!! i'm very stuck on this and don't know how to work it out.

please also try to keep it simple so i can understand thank you.