To regroup the extra tens block in the division of \(66 \div 5\), we look at the number 66.
66 can be broken down into 60 (which is 6 tens) and 6 ones. If you were to regroup the 60 into ones, you'd convert the 6 tens into 60 ones.
So, you can regroup the extra tens block into 60 ones.
Therefore, the filled blank would be: 60.