What comes next? For 8 year olds

Question

This question is from the homework of my niece. She is 8 years old. And I could not help her with this question.

There are 5 x 3 cells. And there is a number in each cell. Problem asks what should be the "?" It should be one of 62, 76, ,79, 81. But I could not find a rule.

5, 4, 11
3, 7, 46
8, 6, 28
4, 5, 21
2, 9, ?

Any ideas? I remind you again. This is a homework for an 8 years old kid. So the rule should be simple but I am in vain.

Answer 1

Square the second number and subtract the first.