Răspuns :
7+7+7+7+7+7=42
42-7-7-7-7-7-7-7=6
56-8-8-8-8-8-8-8-8=7
28-4-4-4-4=7
6+6+6+6+6+6+6+6+6=54
7+7+7=21
42-7-7-7-7-7-7-7=6
56-8-8-8-8-8-8-8-8=7
28-4-4-4-4=7
6+6+6+6+6+6+6+6+6=54
7+7+7=21