So we need to round to the nearest ten with the result being 3450. When rounding to the nearest 10 we look to the ones place. If the ones place is 5 or higher we round up to the next 10. So the highest we can go is 3454 which rounds down to 3450. If we would have gone 1 more higher to 3455 then it would have rounded up to 3460.
So the highest possible number of pens would be
3454.