Mark plants a beanstalk below his second-story window, which is 20 feet off the ground. The beanstalk doubles its height every day. If the beanstalk starts out 4 feet tall, how many days will it take to be taller than Mark's window?
To find the beanstalk's height after one day, multiply the starting height by 2: 4 feet * 2 = 
<gadget id="calculator">4*2</gadget>
<output>8</output>
8 feet.
To find its height after two days, multiply the height after one day by 2: 8 feet * 2 = 
<gadget id="calculator">8*2</gadget>
<output>16</output>
16 feet.
To find its height after three days, multiply the height after two days by 2: 16 feet * 2 = 
<gadget id="calculator">16*2</gadget>
<output>32</output>
32 feet. This is taller than the window, so it took three days for the beanstalk to pass the window.

<result>3</result>