Since the baker had 24 boxes and made 526 donuts, to split them evenly between the total number of boxes means that we need to divide the number of total donuts by the number of boxes:
526 ÷ 24 = 21 remainder of 22
Since 24 x 21 = 504 and 24 x 22 = 528 and the baker only made 526 donuts, then the most amount of donuts he can use to split them evenly with the total amount of 526 is 504. 526 - 504 = 22, so he has an extra 22 donuts that will not be in boxes.