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?
He uses 1 packet per cup of coffee and he has 2 cups a day so that's 1*2 = 
<gadget id="calculator">1*2</gadget>
<output>2</output>
2 packets.
He wants enough to last him 90 days and he uses 2 packets a day so that's 90*2 = 
<gadget id="calculator">90*2</gadget>
<output>180</output>
180 packets.
The packets come 30 to a box and he needs 180 packets so that's 180/30 = 
<gadget id="calculator">180/30</gadget>
<output>6</output>
6 boxes of sugar substitute.
Each box costs $4.00 and he needs 6 boxes so that's 4*6 = $
<gadget id="calculator">4*6</gadget>
<output>24</output>
24.00.

<result>24</result>