Regrouping in subtraction means that if you can't subtract because the digit on the bottom has a greater value than the digit on the top (such as 3-6)m so in this case you would have to regroup twice.
To subtract 426 from 913, you would need to regroup twice. The first regrouping occurs when subtracting in the units place (3 - 6), and the second occurs in the tens place (0 - 2). After regrouping, the final answer is 487.
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