The cost of the food is $3 + $2 + $2 + $2 = $<<3+2+2+2=9>>9.
The original total cost, including tax is $9 + $1 = $<<9+1=10>>10.
Ben increases the total cost to $10 + $2 + $2 = $<<10+2+2=14>>14.
They should get $15 - $14 = $<<15-14=1>>1 in change.
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