Alex has 4 pens in the first week of a month. Every week her pen collection doubles. How many more pens will Alex have than Jane if Jane will have 16 pens after a month?
If Alex has 4 pens in the first week of a month, she will have 4*2 = 
<gadget id="calculator">4*2</gadget>
<output>8</output>
8 pens in the second week.
After her pen collection doubles in the third week, Alex will have 2*8 = 
<gadget id="calculator">2*8</gadget>
<output>16</output>
16 pens.
In the last week of the month, Alex will have 2*16 = 
<gadget id="calculator">2*16</gadget>
<output>32</output>
32 pens after her pen collection.
If Jane has 16 pens after a month, Alex will have 32-16 = 
<gadget id="calculator">32-16</gadget>
<output>16</output>
16 more pens than Jane.

<result>16</result>