He needs food for 21 days because 3 x 7 = <<3*7=21>>21
The puppy will eat 7 cups of food because 21 x (1/3) = <<21*(1/3)=7>>7
He needs 2 bags of food because 7 / 3.5 = <<7/3.5=2>>2
The food will cost him $4 because 2 x 2 = <<2*2=4>>4
It will cost $14 in total because 10 + 4 = <<10+4=14>>14
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