The reason there will be a 6 in the hundredth's place is that there is nothing in the hundredths place in the minuend (number we are subtracting from). We can consider this a zero. Since the subtrahend (the number we are subtracting) has a 4, only 4 + 6 could give us the zero.
8.50 - 4.64 - notice that only a 6 could give us the zero in 8.50.
You would need 15 boxes because when you divide 4070 by 275 you get 14.8 boxes. So with that in mind you cannot have an eighth of a box so you round up to the nearest whole number which in this case is 15 boxes.
