66400 ÷ 7 = 9485 R5
Let's divide 66400 by 7.

Step 1:
7 goes into 6 0 times with a remainder of 6.
Write down 0 as next digit of of the result. 
Result so far: 0
Subtract 0 from 6 to get 6.
Bring next digit (6) of the dividend behind the 6 and repeat the process: 66 / 7

Step 2:
7 goes into 66 9 times with a remainder of 3.
Write down 9 as next digit of of the result. 
Result so far: 9
Subtract 63 from 66 to get 3.
Bring next digit (4) of the dividend behind the 3 and repeat the process: 34 / 7

Step 3:
7 goes into 34 4 times with a remainder of 6.
Write down 4 as next digit of of the result. 
Result so far: 94
Subtract 28 from 34 to get 6.
Bring next digit (0) of the dividend behind the 6 and repeat the process: 60 / 7

Step 4:
7 goes into 60 8 times with a remainder of 4.
Write down 8 as next digit of of the result. 
Result so far: 948
Subtract 56 from 60 to get 4.
Bring next digit (0) of the dividend behind the 4 and repeat the process: 40 / 7

Step 5:
7 goes into 40 5 times with a remainder of 5.
Write down 5 as next digit of of the result. 
Result so far: 9485
Subtract 35 from 40 to get 5.

The final result is 9485 with a remainder of 5.