need to create a number system using only: A=1, B=2, C=3, D=4 and Zero=0. Help

Answer 1

0
1
2
3
4

1 0 = 5 = 5^1 + 0
1 1 = 6 = 5^1 + 1
1 2 = 7 = 5^1 + 2
1 3 = 8
1 4 = 9

2 0 = 10 = 2*5^1 + 0 *5^0
2 1 = 11 = 2*5^1 + 1 *5^0
2 2 = 12 = 2*5^1 + 2 *5^0
etc
...
2 3 1 = 70 = 2*5^2 + 3*5^1 + 1*5^0

Now put in A for 1, B for 2, C for 3 etc
so for example
2 3 1 is B C A

Answer 2

2 3 1 = 66 = 2*5^2 + 3*5^1 + 1*5^0

Now put in A for 1, B for 2, C for 3 etc
so for example
2 3 1 is B C A