2121 ÷ 7 = 303 R0
Alright, let's work through the division of 2121 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 (2) of the dividend behind the 0 and repeat the process: 2 / 7

Step 3:
7 goes into 2 0 times with a remainder of 2.
Write down 0 as next digit of of the result. 
Result so far: 30
Subtract 0 from 2 to get 2.
Bring next digit (1) of the dividend behind the 2 and repeat the process: 21 / 7

Step 4:
7 goes into 21 3 times with a remainder of 0.
Write down 3 as next digit of of the result. 
Result so far: 303
Subtract 21 from 21 to get 0.

The final result is 303 with a remainder of 0.