He planned on 2 sodas per guest and invited 15 guests so 2*15 =<<2*15=30>>30 cans of soda
Each pack of soda had 6 cans. He needed to buy 30 cans of soda for his guest so 30/6 = <<30/6=5>>5 packs of soda
The soda was on sale for $3.00 per 6 pack and he was buying 5 packs so 3*5 = $<<3*5=15.00>>15.00 for soda
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