You can figure out how many boxes Carl will need by dividing the total number of DVDs by the amount of DVDs each box can hold.
Your equation should be: 512 รท 20 = x (amount of boxes needed)
512/20 = 25.6
We will round 25.6 up because you cannot have a fraction of a box, so 25.6 becomes 26.
Carl will need 26 boxes.