First off, 3479 ÷ 21 is 165.666667. There is not much that can be done to figure out how to write 165.666667 as a fraction, except to literally use what the decimal portion of your number, the 0.666667.
Since there are 6 digits in 666667, the very last digit is the "1000000th" decimal place.
Just say that .666667 is the same as 666667/1000000.
So your final answer is: 165
.
Hope I helped, please do contact me if you need more help.