COMPUTER ORGANIZATION QUESTION

I do not understand the leaf procedure in a system not sure how to solve this problem.. HELP and please show me how it is solved.

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Leaf procedure complete the code for stack contents for save registers and return result from $s3 to $v0.

MIPS code:

leaf_example:

add $s0, $a0, $a1

add $s1, $a2, $a3 sub $s2, $s0, $s1

add $s3, $s2, $s2