What is the highest four digit number that when you add up its digits, it equals the sum of the digits in the value of x in the following equation: 9^(-3)*x=9.
x = 6561 its sum=18, the largest 4-digit number=9810. Its sum=18
x = 6561 its sum=18, the largest 4-digit number=9900. Its sum=18
+1904 
