Carl buys index cards for his class.  He gives each student 10 index cards.  He teaches 6 periods a day and each class has 30 students.  If a 50 pack of index cards cost $3 how much did he spend on them all?
He has 30*6=<<30*6=180>>180 students
So he needs to buy 180*10=<<180*10=1800>>1800 index cards
That means he needs to buy 1800/50=<<1800/50=36>>36 packs of index cards
So he spends 36*3=$<<36*3=108>>108
#### 108