Statements: Some bricks are trees. All trees are pens. All pens are boats. Conclusions:  Some boats are bricks. Some pens are bricks. Some trees are bricks. Some bricks are boats.

III is the converse of the first premise and so it holds.

Some bricks are trees. All trees are pens.

Since one premise is particular, the conclusion must be particular and should not contain the middle term. So, it follows that 'Some bricks are pens'. II is the converse of this conclusion and so it holds.

All trees are pens. All pens are boats.

Since both the premises are universal and affirmative, the conclusion must be universal affirmative and should not contain the middle term. So, it follows that 'All trees are boats'.

Some bricks are trees. All trees are boats.

Since one premise is particular, the conclusion must be particular and should not contain the middle term. So, it follows that 'Some bricks are boats'. Thus, IV follows. I is the converse of this conclusion and so it also holds.