He uses 1 packet per cup of coffee and he has 2 cups a day so that's 1*2 = <<1*2=2>>2 packets

He wants enough to last him 90 days and he uses 2 packets a day so that's 90*2 = <<90*2=180>>180 packets

The packets come 30 to a box and he needs 180 packets so that's 180/30 = <<180/30=6>>6 boxes of sugar substitute

Each box costs $4.00 and he needs 6 boxes so that's 4*6 = $<<4*6=24.00>>24.00

# Answer

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<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
Christopher uses 1 packet of a sugar substitute in his coffee.  He has 2 coffees a day.  The packets come 30 to a box and cost $4.00 a box.  How much will it cost him to have enough sugar substitutes to last him 90 days?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
24
Christopher uses 1 packet of a sugar substitute in his coffee.  He has 2 coffees a day.  The packets come 30 to a box and cost $4.00 a box.  How much will it cost him to have enough sugar substitutes to last him 90 days?
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