90399 ÷ 9 = 10044 R3
We're going to perform division on 90399 with 9 as the divisor.

Step 1:
9 goes into 9 1 times with a remainder of 0.
Write down 1 as next digit of of the result. 
Result so far: 1
Subtract 9 from 9 to get 0.
Bring next digit (0) of the dividend behind the 0 and repeat the process: 0 / 9

Step 2:
9 goes into 0 0 times with a remainder of 0.
Write down 0 as next digit of of the result. 
Result so far: 10
Subtract 0 from 0 to get 0.
Bring next digit (3) of the dividend behind the 0 and repeat the process: 3 / 9

Step 3:
9 goes into 3 0 times with a remainder of 3.
Write down 0 as next digit of of the result. 
Result so far: 100
Subtract 0 from 3 to get 3.
Bring next digit (9) of the dividend behind the 3 and repeat the process: 39 / 9

Step 4:
9 goes into 39 4 times with a remainder of 3.
Write down 4 as next digit of of the result. 
Result so far: 1004
Subtract 36 from 39 to get 3.
Bring next digit (9) of the dividend behind the 3 and repeat the process: 39 / 9

Step 5:
9 goes into 39 4 times with a remainder of 3.
Write down 4 as next digit of of the result. 
Result so far: 10044
Subtract 36 from 39 to get 3.

The final result is 10044 with a remainder of 3.