let's use x as the number:
there. from 9 which is the greatest digit. and no repeated numbers, so its down to 6
to round a number you must find the digit next to the said place value
so in 789,215 the said place value is the thousands place so the number we must focus is 2 because 2 is next to 9.
if the focused number is equal or more than 5 you must change the focused number and the digits before the focused number will be turned to zero and the said place value will be added by 1
if the focused number is less than 5 the focused number and the digits before them will be turned to zero.
since the focused number is 2 we must change number 2 to zero and the numbers before them.
therefore the answer is 789,000
round to the nearest tens
round to the nearest ten thousands
round to the nearest hundreds