51 ÷ 3 = 17 R0
No problem, we've got 51 and 3 for the division.

Step 1:
3 goes into 5 1 times with a remainder of 2.
Write down 1 as next digit of of the result. 
Result so far: 1
Subtract 3 from 5 to get 2.
Bring next digit (1) of the dividend behind the 2 and repeat the process: 21 / 3

Step 2:
3 goes into 21 7 times with a remainder of 0.
Write down 7 as next digit of of the result. 
Result so far: 17
Subtract 21 from 21 to get 0.

The final result is 17 with a remainder of 0.