21066 ÷ 7 = 3009 R3
Alright, let's work through the division of 21066 by 7 step by step.

Step 1:
7 goes into 2 0 times with a remainder of 2.
Write down 0 as next digit of of the result. 
Result so far: 0
Subtract 0 from 2 to get 2.
Bring next digit (1) of the dividend behind the 2 and repeat the process: 21 / 7

Step 2:
7 goes into 21 3 times with a remainder of 0.
Write down 3 as next digit of of the result. 
Result so far: 3
Subtract 21 from 21 to get 0.
Bring next digit (0) of the dividend behind the 0 and repeat the process: 0 / 7

Step 3:
7 goes into 0 0 times with a remainder of 0.
Write down 0 as next digit of of the result. 
Result so far: 30
Subtract 0 from 0 to get 0.
Bring next digit (6) of the dividend behind the 0 and repeat the process: 6 / 7

Step 4:
7 goes into 6 0 times with a remainder of 6.
Write down 0 as next digit of of the result. 
Result so far: 300
Subtract 0 from 6 to get 6.
Bring next digit (6) of the dividend behind the 6 and repeat the process: 66 / 7

Step 5:
7 goes into 66 9 times with a remainder of 3.
Write down 9 as next digit of of the result. 
Result so far: 3009
Subtract 63 from 66 to get 3.

The final result is 3009 with a remainder of 3.