To round 6.4 to the nearest whole number, we look at the digit in the tenths place, which is 4.
According to rounding rules, if the digit in the tenths place is 5 or greater, we round up. If it’s less than 5, we round down. Since 4 is less than 5, we round down.
Therefore, 6.4 rounded to the nearest whole number is 6.