668748 is about 670000 when rounded to the nearest blank.
To solve this, we need to look at the number 670000 and think about the rounding process. When we round to a certain place value, everything to the right of that becomes a zero. In this case, everything to the right of the digit seven is a zero. And that means that the place value of that seven is where we rounded to.
This seven is in the ten thousands place. And that means we took 668748 and rounded it to the nearest ten thousand.