12. (a)

4	*	*	*	6	*	*	*	8
*	*	10	*	*	*	14	*	*
*	14	*	16	*	20	*	22	*

(b)

6	*	*	*	9	*	*	*	12
*	*	15	*	*	*	21	*	*
*	21	*	24	*	30	*	33	*

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