10p is not a digit. A digit is an integer in the range 0-9.
Leaving that aside, you can make 31 sums from the 5 coins. If you allow 0 as a valid sum, the answer is 32.
Yuo can make only one combination of 30 digits using 30 digits.
Twelve of them.
24
18 of them.
It is possible to create infinitely many numbers, of infinitely many different lengths, using the digits of the given number. Using each of the digits, and only once, there are 5! = 120 different permutations.
Using only positive digits, and disregarding their order, 3 ways.
If you want 4-digit numbers, there are 24 of them.
If you use them only once each, you can make 15 combinations. 1 with all four digits, 4 with 3 digits, 6 with 2 digits, and 4 with 1 digit. There is also a combination containing no digits making 16 = 24 combinations from 4 elements.
0
6 for 3-digits, 6 for 2-digits, 3 for 1-digits, and 15 for all of the combinations
Six: 234, 243, 324, 342, 423, and 432.
9